Biochemistry, Genetics and Molecular Biology › Cell Biology

Cellular transport and secretion

Works Count: 51460

Wikipedia

Description

This cluster of papers explores the intricate mechanisms involved in intracellular membrane trafficking, including endocytosis, membrane fusion, the roles of Rab proteins and SNARE proteins, the function of ESCRT machinery, the impact of phosphoinositides, and the biogenesis of lysosomes. It covers a wide range of processes such as vesicle traffic, lysosome biogenesis, and the molecular machinery involved in clathrin-mediated endocytosis.

Keywords

Endocytosis; Membrane Fusion; Rab Proteins; Clathrin-Mediated Endocytosis; SNARE Proteins; ESCRT Machinery; Phosphoinositides; Vesicle Traffic; Lysosome Biogenesis; Dynamin

The third helix of the Antennapedia homeodomain translocates through biological membranes.

1994-04-01

Daniele Derossi , Alain Joliot , Gérard Chassaing +1 more

The 60-amino acid long homeodomain of Antennapedia crosses biological membranes by an energy-independent mechanism, a phenomenon abolished by directed mutagenesis within the polypeptide C-terminal region. This finding led us to … The 60-amino acid long homeodomain of Antennapedia crosses biological membranes by an energy-independent mechanism, a phenomenon abolished by directed mutagenesis within the polypeptide C-terminal region. This finding led us to study the internalization of several chemically synthesized peptides derived from the third helix of the homeodomain. We report here that a polypeptide of 16 amino acids in length corresponding to the third helix of the homeodomain deleted of its N-terminal glutamate is still capable of translocating through the membrane. A longer peptide of 20 amino acids also translocates, whereas shorter peptides (15 amino acids) are not internalized by the cells. As is also the case for the entire homeodomain, the 20- and 16-amino acid long peptides are internalized at 4 degrees C, suggesting an energy-independent mechanism of translocation not involving classical endocytosis. The two translocated peptides can be recovered, intact, within the cells, strongly suggesting that they are not targeted to the lysosomal compartment. Finally, substitution of two tryptophans by two phenylalanines strongly diminishes translocation, raising the possibility that the internalization of the third helix is not solely based on its general hydrophobicity.

Rab proteins as membrane organizers

2001-02-01

Marino Zerial , Heidi M. McBride

Crystal structure of a SNARE complex involved in synaptic exocytosis at 2.4 Å resolution

1998-09-01

R. Bryan Sutton , Dirk Fasshauer , Reinhard Jahn +1 more

The Mechanisms of Vesicle Budding and Fusion

2004-01-01

Juan S. Bonifacino , Benjamin S. Glick

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A protein assembly-disassembly pathway in vitro that may correspond to sequential steps of synaptic vesicle docking, activation, and fusion

1993-11-01

Thomas Söllner , Mark K. Bennett , Sidney W. Whiteheart +2 more

Rab GTPases as coordinators of vesicle traffic

2009-07-15

Harald Stenmark

SNAREs — engines for membrane fusion

2006-08-16

Reinhard Jahn , Richard H. Scheller

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The GTPase superfamily: a conserved switch for diverse cell functions

1990-11-01

Henry R. Bourne , D.A.R. Sanders , Frank McCormick

Receptor-mediated endocytosis of transferrin and recycling of the transferrin receptor in rat reticulocytes.

1983-08-01

Clifford V. Harding , John E. Heuser , Philip D. Stahl

At 4 degrees C transferrin bound to receptors on the reticulocyte plasma membrane, and at 37 degrees C receptor-mediated endocytosis of transferrin occurred. Uptake at 37 degrees C exceeded binding … At 4 degrees C transferrin bound to receptors on the reticulocyte plasma membrane, and at 37 degrees C receptor-mediated endocytosis of transferrin occurred. Uptake at 37 degrees C exceeded binding at 4 degrees C by 2.5-fold and saturated after 20-30 min. During uptake at 37 degrees C, bound transferrin was internalized into a trypsin-resistant space. Trypsinization at 4 degrees C destroyed surface receptors, but with subsequent incubation at 37 degrees C, surface receptors rapidly appeared (albeit in reduced numbers), and uptake occurred at a decreased level. After endocytosis, transferrin was released, apparently intact, into the extracellular space. At 37 degrees C colloidal gold-transferrin (AuTf) clustered in coated pits and then appeared inside various intracellular membrane-bounded compartments. Small vesicles and tubules were labeled after short (5-10 min) incubations at 37 degrees C. Larger multivesicular endosomes became heavily labeled after longer (20-35 min) incubations. Multivesicular endosomes apparently fused with the plasma membrane and released their contents by exocytosis. None of these organelles appeared to be lysosomal in nature, and 98% of intracellular AuTf was localized in acid phosphatase-negative compartments. AuTf, like transferrin, was released with subsequent incubation at 37 degrees C. Freeze-dried and freeze-fractured reticulocytes confirmed the distribution of AuTf in reticulocytes and revealed the presence of clathrin-coated patches amidst the spectrin coating the inner surface of the plasma membrane. These data suggest that transferrin is internalized via coated pits and vesicles and demonstrate that transferrin and its receptor are recycled back to the plasma membrane after endocytosis.

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Pathways of clathrin-independent endocytosis

2007-07-04

Satyajit Mayor , Richard E. Pagano

Mechanisms of intracellular protein transport

1994-11-01

James E. Rothman

Intracellular Aspects of the Process of Protein Synthesis

1975-08-01

George E. Palade

The title of the Nobel Lecture of George Palade (1 August, p. 347) should have been Intracellular aspects of the process of protein secretion. The title of the Nobel Lecture of George Palade (1 August, p. 347) should have been Intracellular aspects of the process of protein secretion.

Lysosomes: fusion and function

2007-07-18

J. Paul Luzio , Paul R. Pryor , Nicholas A. Bright

Molecular mechanism and physiological functions of clathrin-mediated endocytosis

2011-07-22

Harvey T. McMahon , Emmanuel Boucrot

Membrane Fusion: Grappling with SNARE and SM Proteins

2009-01-22

Thomas C. Südhof , James E. Rothman

The two universally required components of the intracellular membrane fusion machinery, SNARE and SM (Sec1/Munc18-like) proteins, play complementary roles in fusion. Vesicular and target membrane-localized SNARE proteins zipper up into … The two universally required components of the intracellular membrane fusion machinery, SNARE and SM (Sec1/Munc18-like) proteins, play complementary roles in fusion. Vesicular and target membrane-localized SNARE proteins zipper up into an alpha-helical bundle that pulls the two membranes tightly together to exert the force required for fusion. SM proteins, shaped like clasps, bind to trans-SNARE complexes to direct their fusogenic action. Individual fusion reactions are executed by distinct combinations of SNARE and SM proteins to ensure specificity, and are controlled by regulators that embed the SM-SNARE fusion machinery into a physiological context. This regulation is spectacularly apparent in the exquisite speed and precision of synaptic exocytosis, where synaptotagmin (the calcium-ion sensor for fusion) cooperates with complexin (the clamp activator) to control the precisely timed release of neurotransmitters that initiates synaptic transmission and underlies brain function.

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SNAREpins: Minimal Machinery for Membrane Fusion

1998-03-01

Thomas Weber , Boris V. Zemelman , James A. McNew +5 more

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Ragulator-Rag Complex Targets mTORC1 to the Lysosomal Surface and Is Necessary for Its Activation by Amino Acids

2010-04-01

Yasemin Sancak , Liron Bar‐Peled , Roberto Zoncu +3 more

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Membrane recognition by phospholipid-binding domains

2008-01-23

Mark A. Lemmon

The synaptic vesicle cycle: a cascade of protein–protein interactions

1995-06-01

Thomas C. Südhof

Intracellular protein topogenesis

1980-03-01

Günter Blobel

Concurrently with or shortly after their synthesis on ribosomes, numerous specific proteins are unidirectionally translocated across or asymmetrically integrated into distinct cellular membranes. Thereafter, subpopulations of these proteins need to … Concurrently with or shortly after their synthesis on ribosomes, numerous specific proteins are unidirectionally translocated across or asymmetrically integrated into distinct cellular membranes. Thereafter, subpopulations of these proteins need to be sorted from each other and routed for export or targeted to other intracellular membranes or compartments. It is hypothesized here that the information for these processes, termed "protein topogenesis," is encoded in discrete "topogenic" sequences that constitute a permanent or transient part of the polypeptide chain. The repertoire of distinct topogenic sequences is predicted to be relatively small because many different proteins would be topologically equivalent-i.e., targeted to the same intracellular address. The information content of topogenic sequences would be decoded and processed by distinct effectors. Four types of topogenic sequences could be distinguished: signal sequences, stop-transfer sequences, sorting sequences, and insertion sequences. Signal sequences initiate translocation of proteins across specific membranes. They would be decoded and processed by protein translocators that, by virtue of their signal sequence-specific domain and their unique location in distinct cellular membranes, effect unidirectional translocation of proteins across specific cellular membranes. Stop-transfer sequences interrupt the translocation process that was previously initiated by a signal sequence and, by excluding a distinct segment of the polypeptide chain from translocation, yield asymmetric integration of proteins into translocation-competent membranes. Sorting sequences would act as determinants for posttranslocational traffic of subpopulations of proteins, originating in translocation-competent donor membranes (and compartments) and going to translocation-incompetent receiver membranes (and compartments). Finally, insertion sequences initiate unilateral integration of proteins into the lipid bilayer without the mediation of a distinct protein effector. Examples are given for topogenic sequences, either alone or in combination, to provide the information for the location of proteins in any of the intracellular compartments or for the asymmetric orientation of proteins and their location in any of the cellular membranes. Proposals are made concerning the evolution of topogenic sequences and the relationship of protein topogenesis to the precellular evolution of membranes and compartments.

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A novel arachidonic acid-selective cytosolic PLA2 contains a Ca2+-dependent translocation domain with homology to PKC and GAP

1991-06-01

James D. Clark , Lih‐Ling Lin , Ronald Kriz +5 more

Brefeldin A: insights into the control of membrane traffic and organelle structure.

1992-03-01

Richard D. Klausner , Julie G. Donaldson , Jennifer Lippincott‐Schwartz

THE definition of cellular organelles has evolved over the last hundred years largely driven by morphologic observations, but more recently has been supplemented and complemented by functional and biochemical studies … THE definition of cellular organelles has evolved over the last hundred years largely driven by morphologic observations, but more recently has been supplemented and complemented by functional and biochemical studies (Palade, 1975) . Thus, organelles are now identified both by their morphology and by the set ofcomponents that comprise them . Determining how organelle identity is established and maintained and how newly synthesized protein and membrane are sorted to different organelles are the central issues of organellogenesis . Essential to the many cellular functions that take place within the central vacuolar system (which consists ofthe ER, Golgi apparatus, secretory vesicles, endosomes, and lysosomes) is membrane traffic which mediates the exchange of components between different organelles . There are two critical characteristics of membrane traffic . First, only certain sets oforganelles exchange membrane and the patterns of this exchange define what are called membrane pathways . Second, multiple pathways intersect at specific points within the central vacuolar system . For specific components to choose the correct pathway at such points of crossing, mechanisms exist to impose choices on specific molecules . This process is called sorting . The characteristicsofeachorganelle within the central vacuolar system are likely to be intimately tied to the properties ofmembrane traffic . An imbalance in the magnitude ofmembrane input into and egress from an organelle would have profound effects on the size ofthat compartment . In addition, failures in sorting or aberrations in targeting pathways would be expected to profoundly affect the identity of individual organelles . Recently, the relationship between the control of membrane traffic and the maintenance of organelle structure has been investigated with the use ofa remarkable drug, brefeldin A (BFA).' In this review we will summarize recent findings with BFA and propose some speculative models concerning the mechanism and regulation ofmembrane traffic within the central vacuolar system .

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Identification and localization of synaptophysin, an integral membrane glycoprotein of Mr 38,000 characteristic of presynaptic vesicles

1985-07-01

Bertram Wiedenmann , Werner W. Franke

Lysosome biogenesis and lysosomal membrane proteins: trafficking meets function

2009-08-12

Paul Säftig , Judith Klumperman

A Gene Network Regulating Lysosomal Biogenesis and Function

2009-06-26

Marco Sardiello , Michela Palmieri , Alberto di Ronza +7 more

Master Controller Cellular organelles allow the localized regulation of specialized processes. Under certain conditions, such as increased growth, organelles may be required to alter their function. Coordinated regulation of the … Master Controller Cellular organelles allow the localized regulation of specialized processes. Under certain conditions, such as increased growth, organelles may be required to alter their function. Coordinated regulation of the gene networks required for mitochondrial and endoplasmic reticulum function has been observed. Now, Sardiello et al. (p. 473 ; published online 25 June) have discovered a gene network regulating the lysosome, the major organelle involved in the degradation of internalized macromolecules. Many lysosomal genes were regulated by a single transcription factor, TFEB. TFEB itself can be activated when the lysosome malfunctions and can regulate both the abundance of lysosomes found in the cell, as well as the ability to degrade complex molecules, including a mutant protein that accumulates in patients with Huntington's disease. These results may have implications for the treatment of human lysosomal storage disorders, which are characterized by the aberrant accumulation of macromolecules causing cellular dysfunction.

Endocytosis and the recycling of plasma membrane.

1983-01-01

Ralph M. Steinman , Ira Mellman , William A. Müller +1 more

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Selective stabilisation of developing synapses as a mechanism for the specification of neuronal networks

1976-12-23

Jean‐Pierre Changeux , Antoine Danchin

SNAP receptors implicated in vesicle targeting and fusion

1993-03-25

Thomas Söllner , Sidney W. Whiteheart , Michael Brunner +4 more

Phosphoinositides in cell regulation and membrane dynamics

2006-10-01

Gilbert Di Paolo , Pietro De Camilli

Rapid redistribution of Golgi proteins into the ER in cells treated with brefeldin A: Evidence for membrane cycling from Golgi to ER

1989-03-01

Jennifer Lippincott‐Schwartz , Lydia C. Yuan , Juan S. Bonifacino +1 more

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BAR Domains as Sensors of Membrane Curvature: The Amphiphysin BAR Structure

2003-12-02

Brian J. Peter , Helen M. Kent , Ian G. Mills +4 more

The BAR (Bin/amphiphysin/Rvs) domain is the most conserved feature in amphiphysins from yeast to human and is also found in endophilins and nadrins. We solved the structure of the Drosophila … The BAR (Bin/amphiphysin/Rvs) domain is the most conserved feature in amphiphysins from yeast to human and is also found in endophilins and nadrins. We solved the structure of the Drosophila amphiphysin BAR domain. It is a crescent-shaped dimer that binds preferentially to highly curved negatively charged membranes. With its N-terminal amphipathic helix and BAR domain (N-BAR), amphiphysin can drive membrane curvature in vitro and in vivo. The structure is similar to that of arfaptin2, which we find also binds and tubulates membranes. From this, we predict that BAR domains are in many protein families, including sorting nexins, centaurins, and oligophrenins. The universal and minimal BAR domain is a dimerization, membrane-binding, and curvature-sensing module.

Small GTP-Binding Proteins

2001-01-01

Yoshimi Takai , Takuya Sasaki , Takashi Matozaki

Small GTP-binding proteins (G proteins) exist in eukaryotes from yeast to human and constitute a superfamily consisting of more than 100 members. This superfamily is structurally classified into at least … Small GTP-binding proteins (G proteins) exist in eukaryotes from yeast to human and constitute a superfamily consisting of more than 100 members. This superfamily is structurally classified into at least five families: the Ras, Rho, Rab, Sar1/Arf, and Ran families. They regulate a wide variety of cell functions as biological timers (biotimers) that initiate and terminate specific cell functions and determine the periods of time for the continuation of the specific cell functions. They furthermore play key roles in not only temporal but also spatial determination of specific cell functions. The Ras family regulates gene expression, the Rho family regulates cytoskeletal reorganization and gene expression, the Rab and Sar1/Arf families regulate vesicle trafficking, and the Ran family regulates nucleocytoplasmic transport and microtubule organization. Many upstream regulators and downstream effectors of small G proteins have been isolated, and their modes of activation and action have gradually been elucidated. Cascades and cross-talks of small G proteins have also been clarified. In this review, functions of small G proteins and their modes of activation and action are described.

Dynasore, a Cell-Permeable Inhibitor of Dynamin

2006-06-01

Eric Macia , Marcelo Ehrlich , Ramiro Massol +3 more

Size-dependent internalization of particles via the pathways of clathrin- and caveolae-mediated endocytosis

2004-01-01

Joanna Rejman , Volker Oberle , Inge S. Zuhorn +1 more

Non-phagocytic eukaryotic cells can internalize particles <1 microm in size, encompassing pathogens, liposomes for drug delivery or lipoplexes applied in gene delivery. In the present study, we have investigated the … Non-phagocytic eukaryotic cells can internalize particles <1 microm in size, encompassing pathogens, liposomes for drug delivery or lipoplexes applied in gene delivery. In the present study, we have investigated the effect of particle size on the pathway of entry and subsequent intracellular fate in non-phagocytic B16 cells, using a range of fluorescent latex beads of defined sizes (50-1000 nm). Our data reveal that particles as large as 500 nm were internalized by cells via an energy-dependent process. With an increase in size (50-500 nm), cholesterol depletion increased the efficiency of inhibition of uptake. The processing of the smaller particles was significantly perturbed upon microtubule disruption, while displaying a negligible effect on that of the 500 nm beads. Inhibitor and co-localization studies revealed that the mechanism by which the beads were internalized, and their subsequent intracellular routing, was strongly dependent on particle size. Internalization of microspheres with a diameter <200 nm involved clathrin-coated pits. With increasing size, a shift to a mechanism that relied on caveolae-mediated internalization became apparent, which became the predominant pathway of entry for particles of 500 nm in size. At these conditions, delivery to the lysosomes was no longer apparent. The data indicate that the size itself of (ligand-devoid) particles can determine the pathway of entry. The clathrin-mediated pathway of endocytosis shows an upper size limit for internalization of approx. 200 nm, and kinetic parameters may determine the almost exclusive internalization of such particles along this pathway rather than via caveolae.

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Role of Rab GTPases in Membrane Traffic and Cell Physiology

2011-01-01

Alex H. Hutagalung , Peter Novick

Intracellular membrane traffic defines a complex network of pathways that connects many of the membrane-bound organelles of eukaryotic cells. Although each pathway is governed by its own set of factors, … Intracellular membrane traffic defines a complex network of pathways that connects many of the membrane-bound organelles of eukaryotic cells. Although each pathway is governed by its own set of factors, they all contain Rab GTPases that serve as master regulators. In this review, we discuss how Rabs can regulate virtually all steps of membrane traffic from the formation of the transport vesicle at the donor membrane to its fusion at the target membrane. Some of the many regulatory functions performed by Rabs include interacting with diverse effector proteins that select cargo, promoting vesicle movement, and verifying the correct site of fusion. We describe cascade mechanisms that may define directionality in traffic and ensure that different Rabs do not overlap in the pathways that they regulate. Throughout this review we highlight how Rab dysfunction leads to a variety of disease states ranging from infectious diseases to cancer.

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Sorting of GPI-anchored proteins to glycolipid-enriched membrane subdomains during transport to the apical cell surface

1992-02-01

Deborah A. Brown , John K. Rose

We show that a protein with a glycosylphosphatidyl inositol (GPI) anchor can be recovered from lysates of epithelial cells in a low density, detergent-insoluble form. Under these conditions, the protein … We show that a protein with a glycosylphosphatidyl inositol (GPI) anchor can be recovered from lysates of epithelial cells in a low density, detergent-insoluble form. Under these conditions, the protein is associated with detergent-resistant sheets and vesicles that contain other GPI-anchored proteins and are enriched in glycosphingolipids, but do not contain a basolateral marker protein. The protein is recovered in this complex only after it has been transported to the Golgi complex, suggesting that protein-sphingolipid microdomains form in the Golgi apparatus and plasma membrane and supporting the model proposed by Simons and colleagues for sorting of certain membrane proteins to the apical surface after intracellular association with glycosphingolipids.

ENDOCYTOSIS AND MOLECULAR SORTING

1996-11-01

Ira Mellman

▪ Abstract Endocytosis in eukaryotic cells is characterized by the continuous and regulated formation of prolific numbers of membrane vesicles at the plasma membrane. These vesicles come in several different … ▪ Abstract Endocytosis in eukaryotic cells is characterized by the continuous and regulated formation of prolific numbers of membrane vesicles at the plasma membrane. These vesicles come in several different varieties, ranging from the actin-dependent formation of phagosomes involved in particle uptake, to smaller clathrin-coated vesicles responsible for the internalization of extracellular fluid and receptor-bound ligands. In general, each of these vesicle types results in the delivery of their contents to lysosomes for degradation. The membrane components of endocytic vesicles, on the other hand, are subject to a series of highly complex and iterative molecular sorting events resulting in their targeting to specific destinations. In recent years, much has been learned about the function of the endocytic pathway and the mechanisms responsible for the molecular sorting of proteins and lipids. This review attempts to integrate these new concepts with long-established views of endocytosis to present a more coherent picture of how the endocytic pathway is organized and how the intracellular transport of internalized membrane components is controlled. Of particular importance are emerging concepts concerning the protein-based signals responsible for molecular sorting and the cytosolic complexes responsible for the decoding of these signals.

The Biogenesis of Lysosomes

1989-11-01

Stuart Kornfeld , Ira Mellman

Article de synthese sur les lysosomes: biogenese, definition, role biologique. Les enzymes lysosomales sont decrites ainsi que leur role dans l'exo et l'endocytose. La structure et le biogenese de la … Article de synthese sur les lysosomes: biogenese, definition, role biologique. Les enzymes lysosomales sont decrites ainsi que leur role dans l'exo et l'endocytose. La structure et le biogenese de la membrane lysosomale sont etudiees

Molecular Anatomy of a Trafficking Organelle

2006-11-01

Shigeo Takamori , Matthew G. Holt , Katinka Stenius +7 more

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Ubiquitin-Dependent Sorting into the Multivesicular Body Pathway Requires the Function of a Conserved Endosomal Protein Sorting Complex, ESCRT-I

2001-07-01

David J. Katzmann , Markus Babst , Scott D. Emr

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Signals for Sorting of Transmembrane Proteins to Endosomes and Lysosomes

2003-03-11

Juan S. Bonifacino , Linton M. Traub

▪ Abstract Sorting of transmembrane proteins to endosomes and lysosomes is mediated by signals present within the cytosolic domains of the proteins. Most signals consist of short, linear sequences of … ▪ Abstract Sorting of transmembrane proteins to endosomes and lysosomes is mediated by signals present within the cytosolic domains of the proteins. Most signals consist of short, linear sequences of amino acid residues. Some signals are referred to as tyrosine-based sorting signals and conform to the NPXY or YXXØ consensus motifs. Other signals known as dileucine-based signals fit [DE]XXXL[LI] or DXXLL consensus motifs. All of these signals are recognized by components of protein coats peripherally associated with the cytosolic face of membranes. YXXØ and [DE]XXXL[LI] signals are recognized with characteristic fine specificity by the adaptor protein (AP) complexes AP-1, AP-2, AP-3, and AP-4, whereas DXXLL signals are recognized by another family of adaptors known as GGAs. Several proteins, including clathrin, AP-2, and Dab2, have been proposed to function as recognition proteins for NPXY signals. YXXØ and DXXLL signals bind in an extended conformation to the μ2 subunit of AP-2 and the VHS domain of the GGAs, respectively. Phosphorylation events regulate signal recognition. In addition to peptide motifs, ubiquitination of cytosolic lysine residues also serves as a signal for sorting at various stages of the endosomal-lysosomal system. Conjugated ubiquitin is recognized by UIM, UBA, or UBC domains present within many components of the internalization and lysosomal targeting machinery. This complex array of signals and recognition proteins ensures the dynamic but accurate distribution of transmembrane proteins to different compartments of the endosomal-lysosomal system.

THE SYNAPTIC VESICLE CYCLE

2004-06-24

Thomas C. Südhof

Neurotransmitter release is mediated by exocytosis of synaptic vesicles at the presynaptic active zone of nerve terminals. To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking … Neurotransmitter release is mediated by exocytosis of synaptic vesicles at the presynaptic active zone of nerve terminals. To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle. The focal point of the vesicle cycle is Ca2+-triggered exocytosis that is followed by different routes of endocytosis and recycling. Recycling then leads to the docking and priming of the vesicles for another round of exo- and endocytosis. Recent studies have led to a better definition than previously available of how Ca2+ triggers exocytosis and how vesicles recycle. In particular, insight into how Munc18-1 collaborates with SNARE proteins in fusion, how the vesicular Ca2+ sensor synaptotagmin 1 triggers fast release, and how the vesicular Rab3 protein regulates release by binding to the active zone proteins RIM1 alpha and RIM2 alpha has advanced our understanding of neurotransmitter release. The present review attempts to relate these molecular data with physiological results in an emerging view of nerve terminals as macromolecular machines.

Mechanisms of Endocytosis

2009-03-24

Gary J. Doherty , Harvey T. McMahon

Endocytic mechanisms control the lipid and protein composition of the plasma membrane, thereby regulating how cells interact with their environments. Here, we review what is known about mammalian endocytic mechanisms, … Endocytic mechanisms control the lipid and protein composition of the plasma membrane, thereby regulating how cells interact with their environments. Here, we review what is known about mammalian endocytic mechanisms, with focus on the cellular proteins that control these events. We discuss the well-studied clathrin-mediated endocytic mechanisms and dissect endocytic pathways that proceed independently of clathrin. These clathrin-independent pathways include the CLIC/GEEC endocytic pathway, arf6-dependent endocytosis, flotillin-dependent endocytosis, macropinocytosis, circular doral ruffles, phagocytosis, and trans-endocytosis. We also critically review the role of caveolae and caveolin1 in endocytosis. We highlight the roles of lipids, membrane curvature-modulating proteins, small G proteins, actin, and dynamin in endocytic pathways. We discuss the functional relevance of distinct endocytic pathways and emphasize the importance of studying these pathways to understand human disease processes.

Phosphoinositides: Tiny Lipids With Giant Impact on Cell Regulation

2013-07-01

Tamás Balla

Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as … Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.

Synaptotagmin I: A major Ca2+ sensor for transmitter release at a central synapse

1994-11-01

Martin Geppert , Yukiko Goda , Robert E. Hammer +4 more

Rab Conversion as a Mechanism of Progression from Early to Late Endosomes

2005-09-01

Jochen C. Rink , Éric Ghigo , Yannis Kalaidzidis +1 more

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Regulated portals of entry into the cell

2003-03-01

S. D. Conner , Sandra L. Schmid

Ror2 signaling regulates Golgi structure and transport through IFT20 for tumor invasiveness

2017-01-24

Michiru Nishita , Seung‐Yeol Park , Tadashi Nishio +7 more

Signaling through the Ror2 receptor tyrosine kinase promotes invadopodia formation for tumor invasion. Here, we identify intraflagellar transport 20 (IFT20) as a new target of this signaling in tumors that … Signaling through the Ror2 receptor tyrosine kinase promotes invadopodia formation for tumor invasion. Here, we identify intraflagellar transport 20 (IFT20) as a new target of this signaling in tumors that lack primary cilia, and find that IFT20 mediates the ability of Ror2 signaling to induce the invasiveness of these tumors. We also find that IFT20 regulates the nucleation of Golgi-derived microtubules by affecting the GM130-AKAP450 complex, which promotes Golgi ribbon formation in achieving polarized secretion for cell migration and invasion. Furthermore, IFT20 promotes the efficiency of transport through the Golgi complex. These findings shed new insights into how Ror2 signaling promotes tumor invasiveness, and also advance the understanding of how Golgi structure and transport can be regulated.

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Mechanisms of clathrin-mediated endocytosis

2018-02-07

Marko Kaksonen , Aurélien Roux

Endocytic recycling

2004-01-30

Frederick R. Maxfield , Timothy E. McGraw

Killer Toxin K28 resistance in yeast relies on COG complex mediated trafficking of the defence factor Ktd1

2025-06-25

Kamilla M. E. Laidlaw , Hatwan H. Nadir , Amy Milburn +7 more | Journal of Cell Science

A/B toxins are a diverse family of protein toxins that enter host cells via endocytosis and induce cell death. In yeast, the A/B toxin K28 is internalised to endosomes of … A/B toxins are a diverse family of protein toxins that enter host cells via endocytosis and induce cell death. In yeast, the A/B toxin K28 is internalised to endosomes of susceptible yeast, before following the retrograde trafficking pathway and ultimately triggering cell cycle arrest. The endolysosomal defence factor Ktd1 protects against K28, but its regulation remains unclear. We show all lobe B subunits of the conserved oligomeric Golgi (COG) tethering complex are required for K28 resistance. Our experiments suggest the hypersensitivity of cog mutants is primarily explained by defects in Ktd1 trafficking. Ktd1 mis-localisation in cog mutants is reminiscent to disruptions in Snc1, a surface cargo that recycles multiple times via the Golgi. This work suggests not only that the COG complex is responsible for the precise trafficking of Ktd1 required to mediate toxin defence, but that Ktd1 may survey endolysosomal compartments for toxin. This work underpins the importance of Ktd1 in defence against the A/B toxin K28, and implies how various membrane trafficking regulators could influence toxin effects in other eukaryotic systems.

Interactions between TTYH2 and APOE facilitate endosomal lipid transfer

2025-06-25

A. Sukalskaia , Andreas Karner , Anna Pugnetti +3 more | Nature

Abstract The Tweety homologues (TTYHs) constitute a family of eukaryotic membrane proteins that, on the basis of structural features, were recently proposed to contribute to lipid transfer between soluble carriers … Abstract The Tweety homologues (TTYHs) constitute a family of eukaryotic membrane proteins that, on the basis of structural features, were recently proposed to contribute to lipid transfer between soluble carriers and cellular membranes 1 . However, in the absence of supporting data, this function was hypothetical. Here through pull-down of endogenous proteins, we identify APOE as the interaction partner of human TTYH2. Subcellular fractionation and immunocytochemistry assays showed that both proteins colocalize in endosomal compartments. Characterization of the specific interaction between APOE and TTYH2 through binding assays and structural studies enabled us to identify an epitope in an extended domain of TTYH2 that faces the endosomal lumen. Structures of complexes with APOE-containing lipoprotein particles revealed a binding mode that places lipids in a suitable position to facilitate their diffusion into the membrane. Moreover, in vitro studies revealed that lipid transfer is accelerated by TTYH2. Collectively, our findings indicate that TTYH2 has a role in the unloading of APOE-containing lipoproteins after they are endocytosed. These results define a new protein class that facilitates the extraction of lipids from and their insertion into cellular membranes. Although ubiquitous, this process could be of particular relevance in the brain, where APOE is involved in the transfer of lipids between astrocytes and neurons.

PDZ-directed substrate recruitment is the primary determinant of specific 4E-BP1 dephosphorylation by PP1-Neurabin

2025-06-23

Roman O Fedoryshchak , Karim El-Bouri , Dhira Joshi +2 more | eLife

Phosphoprotein phosphatase 1 (PP1) relies on association with PP1-interacting proteins (PIPs) to generate substrate-specific PIP/PP1 holoenzymes, but the lack of well-defined substrates has hindered elucidation of the mechanisms involved. We … Phosphoprotein phosphatase 1 (PP1) relies on association with PP1-interacting proteins (PIPs) to generate substrate-specific PIP/PP1 holoenzymes, but the lack of well-defined substrates has hindered elucidation of the mechanisms involved. We previously demonstrated that the Phactr1 PIP confers sequence specificity on the Phactr1/PP1 holoenzyme by remodelling the PP1 hydrophobic substrate groove. Phactr1 defines a group of ‘RVxF-ΦΦ-R-W’ PIPs that all interact with PP1 in a similar fashion. Here, we use a PP1-PIP fusion approach to address sequence specificity and identify substrates of the RVxF-ΦΦ-R-W family PIPs. We show that the four Phactr proteins confer identical sequence specificities on their holoenzymes. We identify the 4E-BP and p70 S6K translational regulators as substrates for the Neurabin/Spinophilin PIPs, implicated in neuronal plasticity, pointing to a role for their holoenzymes in mTORC1-dependent translational control. Biochemical and structural experiments show that in contrast to the Phactrs, substrate recruitment and catalytic efficiency of the PP1-Neurabin and PP1-Spinophilin fusions is primarily determined by substrate interaction with the PDZ domain adjoining their RVxF-ΦΦ-R-W motifs, rather than by recognition of the remodelled PP1 hydrophobic groove. Thus, even PIPs that interact with PP1 in a similar manner use different mechanisms to ensure substrate selectivity.

APOE4 triggers dysregulated synaptic vesicle release by disrupting SNARE complex assembly

2025-06-23

Feng Chen , Yanting Chen , Sifan Feng +7 more | Cellular and Molecular Life Sciences

The ε4 allele of the Apolipoprotein E (APOE) gene is an important genetic risk factor for several neurodegenerative diseases, while the common pathogenic mechanism is still unclear. Impaired synaptic transmission … The ε4 allele of the Apolipoprotein E (APOE) gene is an important genetic risk factor for several neurodegenerative diseases, while the common pathogenic mechanism is still unclear. Impaired synaptic transmission is one of the common pathogenic features of neurodegenerative diseases. By using proteomics analysis, co-immunoprecipitation (Co-IP), and bimolecular fluorescence complementation (BiFC) assay, we demonstrated that APOE interacts with VAMP2, a core component of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, in an APOE4 > APOE3 manner. Further in vitro and in vivo results suggest that APOE4 blocks SNARE complex assembly, which is likely driven by liquid-liquid phase separation (LLPS), negatively regulating synaptic vesicle release. Our study shows that APOE4 negatively regulates synaptic vesicle release by blocking the soluble SNARE complex assembly. Our data shed a light on how APOE polymorphism contributes to the risk for neurodegenerative diseases, and provides a theoretical basis for the future APOE targeted treatment of neurological diseases.

The clues offered by SNAREs on the vacuoles of plants and animals

2025-06-23

Fabrizio Barozzi , Miguel Sampaio , Cláudia Pereira +1 more | Frontiers in Plant Science

Vacuoles and lysosome-related organelles (LROs) are essential compartments in eukaryotic cells playing crucial roles in storage, degradation, signaling, and homeostasis. Despite their functional similarities, these organelles have traditionally been studied … Vacuoles and lysosome-related organelles (LROs) are essential compartments in eukaryotic cells playing crucial roles in storage, degradation, signaling, and homeostasis. Despite their functional similarities, these organelles have traditionally been studied in isolation within plant and animal cell biology. This review bridges these disciplines by exploring the molecular parallels between plant vacuoles and animal LROs, with a particular emphasis on the SNARE (Soluble N-ethylmaleimide-sensitive factor Attachment Protein Receptor) protein family, which governs membrane fusion and trafficking. SNARE complexes orchestrate intracellular transport ensuring the correct delivery of cargo to vacuoles and LROs. By analyzing SNARE homologs and their interactions across kingdoms, we highlight conserved mechanisms that regulate organelle biogenesis, remodeling, and function. This comparative approach not only advances our understanding of cellular compartmentalization but also sheds light on potential applications in biotechnology, stress adaptation, and human disease research. Integrating knowledge from plant and animal systems offers a powerful framework for discovering novel regulatory pathways in membrane trafficking and cellular homeostasis.

Evolutionarily diverged on-switch for actin assembly in fungal endocytosis

2025-06-23

Juliette Sebellin , Fabina Binth Kandiyoth , Andrea Picco +5 more | bioRxiv (Cold Spring Harbor Laboratory)

ABSTRACT Clathrin-mediated endocytosis is a conserved eukaryotic trafficking process where an Arp2/3 complex nucleated branched actin network provides force for vesicle formation. The mechanisms that initiate endocytic actin assembly are … ABSTRACT Clathrin-mediated endocytosis is a conserved eukaryotic trafficking process where an Arp2/3 complex nucleated branched actin network provides force for vesicle formation. The mechanisms that initiate endocytic actin assembly are incompletely understood. In the fission yeast, Schizosaccharomyces pombe , actin assembly is initiated by Dip1, an Arp2/3 activator. In the budding yeast, Saccharomyces cerevisiae, the initiation of actin assembly has remained a mystery. Here we show that S. cerevisiae Ldb17, the homolog of Dip1, functions as an on-switch for endocytic actin assembly. Unexpectedly, the regulation of Ldb17 is more complicated than that of constitutively active Dip1. Ldb17 is controlled by a coat protein, Sla1, via separate recruitment and activation steps. This regulation was likely lost in the S. pombe lineage and this simplification may be related to other changes in actin assembly between these species. Our findings add a key missing piece in the understanding of endocytosis in S. cerevisiae and reveal an intriguing evolutionary tinkering of the actin on-switch.

Phosphorylation-Coupled Autoregulation Maintains Functional ER Exit Sites

2025-06-20

Miharu Maeda , Masashi Arakawa , Masaki Wakabayashi +2 more | bioRxiv (Cold Spring Harbor Laboratory)

Abstract Secretory proteins are synthesized in the endoplasmic reticulum (ER) and begin their transport from specialized domains on the ER called ER exit sites (ERES). We previously demonstrated that the … Abstract Secretory proteins are synthesized in the endoplasmic reticulum (ER) and begin their transport from specialized domains on the ER called ER exit sites (ERES). We previously demonstrated that the interaction between TANGO1 and Sec16 is critical for ERES formation. In this study, we reveal that the phosphorylation of TANGO1 and Sec16 is regulated by a FAM83A/CK1α-mediated negative feedback loop. Conversely, their dephosphorylation is regulated in a spatially distinct manner by different phosphatase complexes: PPP6R3/PPP6C for Sec16 and PPP1R15B/PPP1C for TANGO1. Excessive phosphorylation of either TANGO1 or Sec16 leads to ERES disassembly, while excessive dephosphorylation impairs secretion. Our findings demonstrate that maintaining a balanced phosphorylation state of TANGO1 and Sec16 through autoregulation by FAM83A/CK1α and the phosphatases PP1 and PP6 is essential for sustaining proper secretory activity at the ERES.

A Novel Modulator of Resistance for Oxaliplatin-Based Therapy for Colorectal Cancer: The ESCRT Family Member VPS4A

2025-06-19

Noha M. Abdelrazik , Anjana Patel , Andrew Conn +3 more | Cells

Drug resistance is still one of the main challenges for the treatment of colorectal cancer (CRC). Whilst some resistance mechanisms are well known, from the static therapy success rate, clearly, … Drug resistance is still one of the main challenges for the treatment of colorectal cancer (CRC). Whilst some resistance mechanisms are well known, from the static therapy success rate, clearly, still much is undiscovered. Intracellular transport mechanisms have attracted attention as having a possible role in drug resistance, and here, the Endosomal Sorting Complex Required for Transport (ESCRT) protein family is studied as a source of drug resistance modulation using human CRC cell lines and clinical material. From an initial screening of ESCRT proteins in a panel of 10 CRC wild-type cell lines using immunoblotting, Vacuolar Protein Sorting-Associated Protein A4 (VPS4A) was identified as being consistently highly expressed, and it was selected for further investigation. Immunohistopathological evaluation in a small panel of CRC patient samples demonstrated high expression in the tumor epithelium compared to normal intestinal epithelium. The knockdown of VPS4A resulted in enhanced sensitivity of cells to oxaliplatin, and it was subsequently seen that oxaliplatin-resistant sublines had significantly higher VPS4A expression than their wild-type variants. In addition, it was demonstrated that a small molecule inhibitor of VPS4A, aloperine, could interact synergistically with oxaliplatin to enhance its sensitivity in an oxaliplatin-resistant cell line. We hypothesize from initial RNA sequencing analysis that the mechanism of action of VPS4A modulation is through depleting levels of the drug efflux transporter MRP2 in the cell, preventing oxaliplatin egress and increasing cell exposure to the drug. The evidence presented here thus indicates that ESCRT machinery, specifically VPS4A, may act as a modulator of oxaliplatin resistance in CRC.

Potential Roles of SNX17, Rab11, and Rab5 in LDLR Recycling

2025-06-19

Xiaofei Zhao , Shiyin Long , Meiqi Zhu +4 more | Arteriosclerosis Thrombosis and Vascular Biology

Atherosclerotic cardiovascular disease is a leading cause of morbidity and mortality globally. Elevated levels of serum LDL-C (low-density lipoprotein cholesterol) represent a significant risk factor for atherosclerosis. LDLR (low-density lipoprotein … Atherosclerotic cardiovascular disease is a leading cause of morbidity and mortality globally. Elevated levels of serum LDL-C (low-density lipoprotein cholesterol) represent a significant risk factor for atherosclerosis. LDLR (low-density lipoprotein receptor) plays a critical role in LDL-C uptake and clearance, with its recycling to the cell surface being essential for maintaining LDLR availability. However, the molecular mechanisms underlying LDLR homeostasis and recycling remain poorly defined. SNX (sorting nexin) proteins and Rab (Ras-associated binding protein) GTPases are key regulators of vesicle transport and endosomal sorting and are implicated in LDLR endocytosis, recycling, and subsequent cholesterol metabolism. This review aims to summarize the data on the roles of SNX17, Rab11, and Rab5 in LDLR recycling and endosomal dynamics, highlighting their potential as therapeutic targets for managing dyslipidemia and associated diseases.

Lipid Modification and Membrane Localization of Proteins in Cell-Free System

2025-06-19

Rena Matsumoto , Tatsuya Niwa , K. Kuno +3 more | ACS Synthetic Biology

Post-translational modifications are an essential process for proper protein function and localization. In particular, lipid modification plays a crucial role in the spatial regulation of proteins functioning on a lipid … Post-translational modifications are an essential process for proper protein function and localization. In particular, lipid modification plays a crucial role in the spatial regulation of proteins functioning on a lipid membrane surface. While cell-free protein synthesis allows rapid protein production, technical advances in lipidation modification are behind. Here, we developed a cell-free system for the myristoylation and palmitoylation of proteins. Based on our previous study, we improved myristoylation efficiency by trimming a precursor nascent peptide, which undergoes lipidation at the N-terminal glycine. We also found that N-myristoyltransferase (NMT) catalyzes both myristoylation and palmitoylation. The localization of lipidated proteins onto liposomes is further aided by the insertion of polyarginine residues downstream of the NMT recognition site. Finally, we demonstrated that lipidation of VHH antibodies and localization onto liposomes resulted in target-specific binding to cancer cells. This system offers a platform for displaying soluble proteins on lipid membranes, with potential applications in developing liposomes for targeted cell binding.

Characterization of in vivo binding kinetics and non-displaceable binding of [18F]SynvesT-1 in the rat brain

2025-06-18

Catriona Wimberley , Carlos J. Alcaide‐Corral , Timaeus E. F. Morgan +6 more | EJNMMI Research

Abstract Background The synaptic vesicle glycoprotein 2 A (SV2A) has been identified as a biomarker of interest for neurological pathology. The SV2A specific radiotracer [ 18 F]SynVesT-1 has shown good … Abstract Background The synaptic vesicle glycoprotein 2 A (SV2A) has been identified as a biomarker of interest for neurological pathology. The SV2A specific radiotracer [ 18 F]SynVesT-1 has shown good binding characteristics in mouse and human. The aim of this study was to characterize the binding parameters of [ 18 F]SynVesT-1 in the rat brain and investigate simplified quantification methods. Twenty-one Positron Emission Tomography (PET) scans were conducted in male Sprague-Dawley rats with a bolus injection of [ 18 F]SynVesT-1. Varying concentrations of non-radioactive SynVesT-1 were injected in an increasing mass dose paradigm ( n = 21 ) with radioactivity in arterial blood recorded throughout. The radiometabolism was characterized in a further group ( n = 7). The total volume of distribution ( V T ) was estimated using compartmental modelling and Logan plot and then compared to the standardized uptake value at 30–60 min ( SUV 30 − 60 ). Occupancy plots and a Lassen plot were generated. Results The pharmacokinetics of [ 18 F]SynVesT-1 PET showed rapid brain uptake and increasing doses of SynVesT-1 revealed a robust reduction in radiotracer uptake over all brain regions. The two-tissue compartmental model was most appropriate and the estimated V T was highly correlated with Logan V T , as was the SUV 30 − 60 . The V ND was estimated to be 3.75, which is 12.5% (pons) to 22% (thalamus) of the V T . The estimated upper mass limit required to achieve 5% target occupancy is 0.48 µg/kg. Conclusion [ 18 F]SynVesT-1 shows good characteristics for imaging the rat brain, however care must be taken to achieve adequate molar activity to avoid mass dose affects (< 5% occupancy). Data showed no suitable reference region for [ 18 F]SynVesT-1, however SUV 30 − 60 does give an appropriate surrogate for V T . Clinical trial number Not applicable.

YKT6 Is Essential for Male Fertility by Promoting Meiosis Progression During Spermatogenesis of Mice.

2025-06-18

Jie Cen , Xiaochen Yu , Ziqi Wang +6 more | PubMed

SNARE proteins are required for membrane fusion events throughout the endomembrane system, and are therefore associated with vesicular transport. Here, we found that the SNARE family member, YKT6, is indispensable … SNARE proteins are required for membrane fusion events throughout the endomembrane system, and are therefore associated with vesicular transport. Here, we found that the SNARE family member, YKT6, is indispensable for male fertility in mice. Conditional Ykt6 knockout in pre-meiotic and meiotic germ cells leads to complete sterility and meiotic arrest in male mice, which exhibit loss of spermatocytes in seminiferous tubules, but without obvious disruption of chromosomal behaviours during meiosis. We observed that the abundance of syncytia increases along with abnormal morphology of the Golgi apparatus, while lysosomes decrease in Ykt6-cKO testes. Quantitative proteomics and immunofluorescent staining both showed dysregulation of vesicular transport in YKT6-deficient spermatocytes. Additionally, the recombinant mouse proteins, HA::YKT6 and MYC::STX1A, could interact in vitro, further supporting a likely role in mediating transport vesicle fusion with the plasma membrane. Finally, the absence of TEX14 signal within syncytia and enlarged TEX14 rings between spermatocytes together suggest a failure to stabilise intercellular bridges in Ykt6-cKO testes. These results demonstrate that YKT6 is required for male fertility by promoting meiosis progression through vesicular transport regulation during spermatogenesis in mice, expanding our understanding of YKT6 functions, and suggesting a possible strategy for future interventions for male infertility in humans.

From Gene to Pathways: Understanding Novel Vps51 Variant and Its Cellular Consequences

2025-06-14

Damla Aygün , Didem Yücel Yılmaz | International Journal of Molecular Sciences

Disorders of vesicular trafficking and genetic defects in autophagy play a critical role in the development of metabolic and neurometabolic diseases. These processes govern intracellular transport and lysosomal degradation, thereby … Disorders of vesicular trafficking and genetic defects in autophagy play a critical role in the development of metabolic and neurometabolic diseases. These processes govern intracellular transport and lysosomal degradation, thereby maintaining cellular homeostasis. In this article, we present two siblings with a novel homozygous variant in VPS51 (Vacuolar protein sorting 51) gene (c.1511C>T; p.Thr504Met), exhibiting developmental delay, a thin corpus callosum, severe intellectual disability, epilepsy, microcephaly, hearing loss, and dysphagia. This study aimed to investigate the effects of the novel VPS51 gene variation at the RNA and protein level in fibroblasts derived from patients. A comparative proteomic analysis, which has not been previously elucidated, was performed to identify uncharacterized proteins associated with vesicular trafficking. Furthermore, the impact of disrupted pathways on mitochondria-lysosome contact sites was assessed, offering a thorough pathophysiological evaluation of GARP/EARP (Golgi Associated Retrograde Protein / Endosome Associated Retrograde Protein) complex dysfunction. An analysis of mRNA expression indicated decreased levels of the VPS51 gene, alongside modifications in the expression of autophagy-related genes (LC3B, p62, RAB7A, TBC1D15). Western blotting demonstrated a reduction in VPS51 and autophagy-related protein levels. Proteomic profiling revealed 585 differentially expressed proteins, indicating disruptions in vesicular trafficking, lysosomal function, and mitochondrial metabolism. Proteins involved in mitochondrial β-oxidation and oxidative phosphorylation exhibited downregulation, whereas pathways related to glycolysis and lipid synthesis showed upregulation. Live-cell confocal microscopy revealed a notable increase in mitochondria-lysosome contact sites in patient fibroblasts, suggesting that VPS51 protein dysfunction contributes to impaired organelle communication. The findings indicate that the novel VPS51 gene variation influences intracellular transport, autophagy, and metabolic pathways, offering new insights into its involvement in neurometabolic disorders.

A Theoretical and Practical Analysis of Membrane Protein Genes Altered in Neutrophils in Parkinson’s Disease

2025-06-13

Araliz López Pintor , María Teresa Rugeles López , José Daniel Lozada‐Ramírez +6 more | Current Issues in Molecular Biology

Parkinson’s disease (PD) is a major health concern, with no accurate or early diagnostic test available for most patients. Chronic inflammation is a recognized contributor to PD pathogenesis; thus, membrane … Parkinson’s disease (PD) is a major health concern, with no accurate or early diagnostic test available for most patients. Chronic inflammation is a recognized contributor to PD pathogenesis; thus, membrane proteins of inflammatory cells such as neutrophils present an accessible target for detecting early molecular changes. In this study, we conducted a theoretical analysis using the GSE99039 database to identify differentially expressed genes (DEGs) in leukocytes from PD patients. From this, we selected nine top candidates for digital polymerase chain reaction (dPCR) analysis in isolated neutrophils from nine PD patients and nine matched controls. Our results revealed significant upregulation of ORAI3 and CLCN2. Unexpectedly, both ACTB (β-actin) and SNCA (alpha-synuclein) were also upregulated in neutrophils. Notably, this study provides the first evidence of CLCN2 expression in neutrophils and demonstrates the significant upregulation of four genes via dPCR. These genes may serve as potential biomarkers for future research on PD detection.

Skin lamellar bodies: a unique set of lysosome-related organelles

2025-06-09

Sarmistha Mahanty | Frontiers in Cell and Developmental Biology

Skin lamellar bodies (LBs) are crucial for forming and renewing the protective skin barrier, which regulates the body’s internal environment and integrity. LB dysfunction is associated with severe disease conditions … Skin lamellar bodies (LBs) are crucial for forming and renewing the protective skin barrier, which regulates the body’s internal environment and integrity. LB dysfunction is associated with severe disease conditions such as atopic dermatitis, Netherton syndrome and Harlequin ichthyosis, among others. Despite its importance in human physiology, the intracellular origin and biogenesis mechanism of LBs remain largely unknown. LBs are lysosome-related organelles (LRO), a group of cell type-specific organelles having unique structures, cargo content, and function. Classical LROs such as melanosomes, lung lamellar bodies and Weibel-Palade bodies share overlapped molecular machinery/mechanisms and are co-affected in genetic disorders like Hermansky-Pudlak syndrome (HPS) or Chédiak-Higashi syndrome (CHS). In contrast, LBs contain a diverse array of protein and lipid cargo that are notably different from those found in other LROs, and LBs are not reported to be affected in HPS/CHS. LBs form in an advanced differentiation state of keratinocytes while cells are experiencing high ions and low nutrients in their exterior, the plasma membrane (PM) undergoing modifications, and intracellular organelles starting to disappear. This article discusses atypical conditions of LB biogenesis in comparison to classical LROs, which may potentially guide future research on LB biogenesis.

Structural Insights into RAB7A Activation: A Mammalian Perspective on the MON1A-CCZ1 GEF Complex

2025-06-09

| Life Metabolism

A histidine switch regulates pH-dependent filament formation by the caspase-9 CARD

2025-06-03

S.K. Rawal , Đesika Kolarić , Stefan Bohn +6 more | bioRxiv (Cold Spring Harbor Laboratory)

Abstract The caspase activation and recruitment domain (CARD) mediates protein-protein interactions in apoptotic and inflammatory signaling pathways. In humans, more than 30 proteins contain a CARD, several of which have … Abstract The caspase activation and recruitment domain (CARD) mediates protein-protein interactions in apoptotic and inflammatory signaling pathways. In humans, more than 30 proteins contain a CARD, several of which have been reported to polymerize into helical filaments. Here we found that the CARD from the apoptotic protease caspase-9 (C9 CARD ) self assembles into filaments in vitro at physiological pH and salt concentrations. The C9 CARD more readily polymerizes under low-salt or mildly acidic conditions, suggesting a significant role for electrostatic interactions in mediating filament formation. Using NMR spectroscopy, we determined the p K a of the lone histidine residue, H38, which supports a role for histidine protonation in enhancing filament formation. Indeed, mutation of H38 to introduce a positive (H38R) or negative (H38D) charge, or to remove the pH-dependence of the side chain at this site altogether (H38N), dramatically alters the filament propensity of the domain. Using cryo-election microscopy, we determined 3.4- and 3.2-Å structures of the wild-type and H38R C9 CARD filaments, respectively, which provide new insights into the molecular basis of C9 CARD polymerization and its pH dependence via H38.