1
|
Cui L, Li H, Xi Y, Hu Q, Liu H, Fan J, Xiang Y, Zhang X, Shui W, Lai Y. Vesicle trafficking and vesicle fusion: mechanisms, biological functions, and their implications for potential disease therapy. MOLECULAR BIOMEDICINE 2022; 3:29. [PMID: 36129576 PMCID: PMC9492833 DOI: 10.1186/s43556-022-00090-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 07/12/2022] [Indexed: 11/10/2022] Open
Abstract
Intracellular vesicle trafficking is the fundamental process to maintain the homeostasis of membrane-enclosed organelles in eukaryotic cells. These organelles transport cargo from the donor membrane to the target membrane through the cargo containing vesicles. Vesicle trafficking pathway includes vesicle formation from the donor membrane, vesicle transport, and vesicle fusion with the target membrane. Coat protein mediated vesicle formation is a delicate membrane budding process for cargo molecules selection and package into vesicle carriers. Vesicle transport is a dynamic and specific process for the cargo containing vesicles translocation from the donor membrane to the target membrane. This process requires a group of conserved proteins such as Rab GTPases, motor adaptors, and motor proteins to ensure vesicle transport along cytoskeletal track. Soluble N-ethyl-maleimide-sensitive factor (NSF) attachment protein receptors (SNARE)-mediated vesicle fusion is the final process for vesicle unloading the cargo molecules at the target membrane. To ensure vesicle fusion occurring at a defined position and time pattern in eukaryotic cell, multiple fusogenic proteins, such as synaptotagmin (Syt), complexin (Cpx), Munc13, Munc18 and other tethering factors, cooperate together to precisely regulate the process of vesicle fusion. Dysfunctions of the fusogenic proteins in SNARE-mediated vesicle fusion are closely related to many diseases. Recent studies have suggested that stimulated membrane fusion can be manipulated pharmacologically via disruption the interface between the SNARE complex and Ca2+ sensor protein. Here, we summarize recent insights into the molecular mechanisms of vesicle trafficking, and implications for the development of new therapeutics based on the manipulation of vesicle fusion.
Collapse
|
2
|
Prasad R, Zhou HX. Membrane Association and Functional Mechanism of Synaptotagmin-1 in Triggering Vesicle Fusion. Biophys J 2020; 119:1255-1265. [PMID: 32882186 DOI: 10.1016/j.bpj.2020.08.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 07/23/2020] [Accepted: 08/10/2020] [Indexed: 12/23/2022] Open
Abstract
Upon Ca2+ influx, synaptic vesicles fuse with the presynaptic plasma membrane (PM) to release neurotransmitters. Membrane fusion is triggered by synaptotagmin-1, a transmembrane protein in the vesicle membrane (VM), but the mechanism is under debate. Synaptotagmin-1 contains a single transmembrane helix (TM) and two tandem C2 domains (C2A and C2B). This study aimed to use molecular dynamics simulations to elucidate how Ca2+-bound synaptotagmin-1, by simultaneously associating with VM and PM, brings them together for fusion. Although C2A stably associates with VM via two Ca2+-binding loops, C2B has a propensity to partially dissociate. Importantly, an acidic motif in the TM-C2A linker competes with VM for interacting with C2B, thereby flipping its orientation to face PM. Subsequently, C2B readily associates with PM via a polybasic cluster and a Ca2+-binding loop. The resulting mechanistic model for the triggering of membrane fusion by synaptotagmin-1 reconciles many experimental observations.
Collapse
Affiliation(s)
- Ramesh Prasad
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois
| | - Huan-Xiang Zhou
- Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois; Department of Physics, University of Illinois at Chicago, Chicago, Illinois.
| |
Collapse
|
3
|
Nyenhuis SB, Thapa A, Cafiso DS. Phosphatidylinositol 4,5 Bisphosphate Controls the cis and trans Interactions of Synaptotagmin 1. Biophys J 2019; 117:247-257. [PMID: 31301806 DOI: 10.1016/j.bpj.2019.06.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Revised: 05/20/2019] [Accepted: 06/18/2019] [Indexed: 11/28/2022] Open
Abstract
Synaptotagmin 1 acts as the Ca2+ sensor for synchronous neurotransmitter release; however, the mechanism by which it functions is not understood and is presently a topic of considerable interest. Here, we describe measurements on full-length membrane-reconstituted synaptotagmin 1 using site-directed spin labeling in which we characterize the linker region as well as the cis (vesicle membrane) and trans (cytoplasmic membrane) binding of its two C2 domains. In the full-length protein, the C2A domain does not undergo membrane insertion in the absence of Ca2+; however, the C2B domain will bind to and penetrate in trans to a membrane containing phosphatidylinositol 4,5 bisphosphate, even if phosphatidylserine (PS) is present in the cis membrane. In the presence of Ca2+, the Ca2+ binding loops of C2A and C2B both insert into the membrane interface; moreover, C2A preferentially inserts into PS-containing bilayers and will bind in a cis configuration to membranes containing PS even if a phosphatidylinositol 4,5 bisphosphate membrane is presented in trans. The data are consistent with a bridging activity for synaptotagmin 1 in which the two domains bind to opposing vesicle and plasma membranes. The failure of C2A to bind membranes in the absence of Ca2+ and the long unstructured segment linking C2A to the vesicle membrane indicates that synaptotagmin 1 could act to significantly shorten the vesicle-plasma membrane distance with increasing levels of Ca2+.
Collapse
Affiliation(s)
- Sarah B Nyenhuis
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, Virginia
| | - Anusa Thapa
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, Virginia
| | - David S Cafiso
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, Virginia.
| |
Collapse
|
4
|
Abstract
The past few years have resulted in an increased awareness and recognition of the prevalence and roles of intrinsically disordered proteins and protein regions (IDPs and IDRs, respectively) in synaptic vesicle trafficking and exocytosis and in overall synaptic organization. IDPs and IDRs constitute a class of proteins and protein regions that lack stable tertiary structure, but nevertheless retain biological function. Their significance in processes such as cell signaling is now well accepted, but their pervasiveness and importance in other areas of biology are not as widely appreciated. Here, we review the prevalence and functional roles of IDPs and IDRs associated with the release and recycling of synaptic vesicles at nerve terminals, as well as with the architecture of these terminals. We hope to promote awareness, especially among neuroscientists, of the importance of this class of proteins in these critical pathways and structures. The examples discussed illustrate some of the ways in which the structural flexibility conferred by intrinsic protein disorder can be functionally advantageous in the context of cellular trafficking and synaptic function.
Collapse
Affiliation(s)
- David Snead
- From the Department of Biochemistry, Weill Cornell Medicine, New York, New York 10021
| | - David Eliezer
- From the Department of Biochemistry, Weill Cornell Medicine, New York, New York 10021
| |
Collapse
|
5
|
Fealey ME, Binder BP, Uversky VN, Hinderliter A, Thomas DD. Structural Impact of Phosphorylation and Dielectric Constant Variation on Synaptotagmin's IDR. Biophys J 2019; 114:550-561. [PMID: 29414700 DOI: 10.1016/j.bpj.2017.12.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Revised: 11/21/2017] [Accepted: 12/04/2017] [Indexed: 11/28/2022] Open
Abstract
We used time-resolved Förster resonance energy transfer, circular dichroism, and molecular dynamics simulation to investigate the structural dependence of synaptotagmin 1's intrinsically disordered region (IDR) on phosphorylation and dielectric constant. We found that a peptide corresponding to the full-length IDR sequence, a ∼60-residue strong polyampholyte, can sample structurally collapsed states in aqueous solution, consistent with its κ-predicted behavior, where κ is a sequence-dependent parameter that is used to predict IDR compaction. In implicit solvent simulations of this same sequence, lowering the dielectric constant to more closely mimic the environment near a lipid bilayer surface promoted further sampling of collapsed structures. We then examined the structural tendencies of central region residues of the IDR in isolation. We found that the exocytosis-modulating phosphorylation of Thr112 disrupts a local disorder-to-order transition induced by trifluoroethanol/water mixtures that decrease the solution dielectric constant and stabilize helical structure. Implicit solvent simulations on these same central region residues testing the impact of dielectric constant alone converge on a similar result, showing that helical structure is formed with higher probability at a reduced dielectric. In these helical conformers, lysine-aspartic acid salt bridges contribute to stabilization of transient secondary structure. In contrast, phosphorylation results in formation of salt bridges unsuitable for helix formation. Collectively, these results suggest a model in which phosphorylation and compaction of the IDR sequence regulate structural transitions that in turn modulate neuronal exocytosis.
Collapse
Affiliation(s)
- Michael E Fealey
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota
| | - Benjamin P Binder
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota
| | - Vladimir N Uversky
- Department of Molecular Medicine, University of South Florida, Tampa, Florida
| | - Anne Hinderliter
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, Minnesota
| | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota.
| |
Collapse
|
6
|
Biochemical studies of membrane fusion at the single-particle level. Prog Lipid Res 2019; 73:92-100. [PMID: 30611882 DOI: 10.1016/j.plipres.2019.01.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 01/01/2019] [Accepted: 01/02/2019] [Indexed: 01/21/2023]
Abstract
To study membrane fusion mediated by synaptic proteins, proteoliposomes have been widely used for in vitro ensemble measurements with limited insights into the fusion mechanism. Single-particle techniques have proven to be powerful in overcoming the limitations of traditional ensemble methods. Here, we summarize current single-particle methods in biophysical and biochemical studies of fusion mediated by soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and other synaptic proteins, together with their advantages and limitations.
Collapse
|
7
|
MacDougall DD, Lin Z, Chon NL, Jackman SL, Lin H, Knight JD, Anantharam A. The high-affinity calcium sensor synaptotagmin-7 serves multiple roles in regulated exocytosis. J Gen Physiol 2018; 150:783-807. [PMID: 29794152 PMCID: PMC5987875 DOI: 10.1085/jgp.201711944] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 05/07/2018] [Indexed: 12/19/2022] Open
Abstract
MacDougall et al. review the structure and function of the calcium sensor synaptotagmin-7 in exocytosis. Synaptotagmin (Syt) proteins comprise a 17-member family, many of which trigger exocytosis in response to calcium. Historically, most studies have focused on the isoform Syt-1, which serves as the primary calcium sensor in synchronous neurotransmitter release. Recently, Syt-7 has become a topic of broad interest because of its extreme calcium sensitivity and diversity of roles in a wide range of cell types. Here, we review the known and emerging roles of Syt-7 in various contexts and stress the importance of its actions. Unique functions of Syt-7 are discussed in light of recent imaging, electrophysiological, and computational studies. Particular emphasis is placed on Syt-7–dependent regulation of synaptic transmission and neuroendocrine cell secretion. Finally, based on biochemical and structural data, we propose a mechanism to link Syt-7’s role in membrane fusion with its role in subsequent fusion pore expansion via strong calcium-dependent phospholipid binding.
Collapse
Affiliation(s)
| | - Zesen Lin
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| | - Nara L Chon
- Department of Chemistry, University of Colorado, Denver, CO
| | - Skyler L Jackman
- Vollum Institute, Oregon Health & Science University, Portland, OR
| | - Hai Lin
- Department of Chemistry, University of Colorado, Denver, CO
| | | | - Arun Anantharam
- Department of Pharmacology, University of Michigan, Ann Arbor, MI
| |
Collapse
|
8
|
Abstract
This review summarizes current knowledge of synaptic proteins that are central to synaptic vesicle fusion in presynaptic active zones, including SNAREs (soluble N-ethylmaleimide sensitive factor attachment protein receptors), synaptotagmin, complexin, Munc18 (mammalian uncoordinated-18), and Munc13 (mammalian uncoordinated-13), and highlights recent insights in the cooperation of these proteins for neurotransmitter release. Structural and functional studies of the synaptic fusion machinery suggest new molecular models of synaptic vesicle priming and Ca2+-triggered fusion. These studies will be a stepping-stone toward answering the question of how the synaptic vesicle fusion machinery achieves such high speed and sensitivity.
Collapse
Affiliation(s)
- Axel T Brunger
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Jeremy Leitz
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| | - Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Department of Neurology and Neurological Sciences, Department of Structural Biology, Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA;
| |
Collapse
|
9
|
Fealey ME, Thomas DD, Hinderliter A. Enhanced synaptotagmin plasticity derived from pairing intrinsic disorder with synaptic vesicle lipids. Commun Integr Biol 2017. [PMCID: PMC5595411 DOI: 10.1080/19420889.2017.1343772] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Synaptotagmin 1 (Syt 1) is an integral membrane protein responsible for sensing the calcium ion (Ca2+) influx in neurons that triggers synaptic vesicle exocytosis. How Syt 1's intrinsically disordered region (IDR), a ∼60 residue sequence located between the protein's transmembrane helix and two Ca2+-sensing C2 domains, contributes to protein function is not well understood. The same is true of analogous IDRs located in the other synaptotagmin isoforms. Recently, we found that the Syt 1 IDR is structurally responsive to vesicles whose lipid composition mimics that of a synaptic vesicle organelle and that this sensitivity allosterically influences binding and folding behavior of the adjacent C2 domain. We believe these observations may be applicable to the study of other synaptotagmin isoforms and discuss generally how an IDR-membrane interaction could contribute to modulation of C2 domain function.
Collapse
Affiliation(s)
- Michael E. Fealey
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota, Minneapolis, MN, USA
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - David D. Thomas
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota, Minneapolis, MN, USA
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Anne Hinderliter
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota, Minneapolis, MN, USA
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| |
Collapse
|
10
|
Zanetti MN, Bello OD, Wang J, Coleman J, Cai Y, Sindelar CV, Rothman JE, Krishnakumar SS. Ring-like oligomers of Synaptotagmins and related C2 domain proteins. eLife 2016; 5. [PMID: 27434670 PMCID: PMC4977156 DOI: 10.7554/elife.17262] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 07/18/2016] [Indexed: 01/25/2023] Open
Abstract
We recently reported that the C2AB portion of Synaptotagmin 1 (Syt1) could self-assemble into Ca(2+)-sensitive ring-like oligomers on membranes, which could potentially regulate neurotransmitter release. Here we report that analogous ring-like oligomers assemble from the C2AB domains of other Syt isoforms (Syt2, Syt7, Syt9) as well as related C2 domain containing protein, Doc2B and extended Synaptotagmins (E-Syts). Evidently, circular oligomerization is a general and conserved structural aspect of many C2 domain proteins, including Synaptotagmins. Further, using electron microscopy combined with targeted mutations, we show that under physiologically relevant conditions, both the Syt1 ring assembly and its rapid disruption by Ca(2+) involve the well-established functional surfaces on the C2B domain that are important for synaptic transmission. Our data suggests that ring formation may be triggered at an early step in synaptic vesicle docking and positions Syt1 to synchronize neurotransmitter release to Ca(2+) influx.
Collapse
Affiliation(s)
- Maria N Zanetti
- Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | - Oscar D Bello
- Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | - Jing Wang
- Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | - Jeff Coleman
- Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | - Yiying Cai
- Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | - Charles V Sindelar
- Department of Molecular Biophysics and Biochemistry, Yale School of Medicine, New Haven, United States
| | - James E Rothman
- Department of Cell Biology, Yale School of Medicine, New Haven, United States
| | | |
Collapse
|
11
|
Fealey ME, Mahling R, Rice AM, Dunleavy K, Kobany SEG, Lohese KJ, Horn B, Hinderliter A. Synaptotagmin I's Intrinsically Disordered Region Interacts with Synaptic Vesicle Lipids and Exerts Allosteric Control over C2A. Biochemistry 2016; 55:2914-26. [PMID: 27191789 DOI: 10.1021/acs.biochem.6b00085] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Synaptotagmin I (Syt I) is a vesicle-localized integral membrane protein that senses the calcium ion (Ca(2+)) influx to trigger fast synchronous release of neurotransmitter. How the cytosolic domains of Syt I allosterically communicate to propagate the Ca(2+) binding signal throughout the protein is not well understood. In particular, it is unclear whether the intrinsically disordered region (IDR) between Syt I's transmembrane helix and first C2 domain (C2A) plays an important role in allosteric modulation of Ca(2+) binding. Moreover, the structural propensity of this IDR with respect to membrane lipid composition is unknown. Using differential scanning and isothermal titration calorimetry, we found that inclusion of the IDR does indeed allosterically modulate Ca(2+) binding within the first C2 domain. Additionally through application of nuclear magnetic resonance, we found that Syt I's IDR interacts with membranes whose lipid composition mimics that of a synaptic vesicle. These findings not only indicate that Syt I's IDR plays a role in regulating Syt I's Ca(2+) sensing but also indicate the IDR is exquisitely sensitive to the underlying membrane lipids. The latter observation suggests the IDR is a key route for communication of lipid organization to the adjacent C2 domains.
Collapse
Affiliation(s)
- Michael E Fealey
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States.,Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Ryan Mahling
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States
| | - Anne M Rice
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States
| | - Katie Dunleavy
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States
| | - Stephanie E G Kobany
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States
| | - K Jean Lohese
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States
| | - Benjamin Horn
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States
| | - Anne Hinderliter
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth , Duluth, Minnesota 55812, United States.,Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota , Minneapolis, Minnesota 55455, United States
| |
Collapse
|
12
|
Phosphorylation of synaptotagmin-1 controls a post-priming step in PKC-dependent presynaptic plasticity. Proc Natl Acad Sci U S A 2016; 113:5095-100. [PMID: 27091977 DOI: 10.1073/pnas.1522927113] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Presynaptic activation of the diacylglycerol (DAG)/protein kinase C (PKC) pathway is a central event in short-term synaptic plasticity. Two substrates, Munc13-1 and Munc18-1, are essential for DAG-induced potentiation of vesicle priming, but the role of most presynaptic PKC substrates is not understood. Here, we show that a mutation in synaptotagmin-1 (Syt1(T112A)), which prevents its PKC-dependent phosphorylation, abolishes DAG-induced potentiation of synaptic transmission in hippocampal neurons. This mutant also reduces potentiation of spontaneous release, but only if alternative Ca(2+) sensors, Doc2A/B proteins, are absent. However, unlike mutations in Munc13-1 or Munc18-1 that prevent DAG-induced potentiation, the synaptotagmin-1 mutation does not affect paired-pulse facilitation. Furthermore, experiments to probe vesicle priming (recovery after train stimulation and dual application of hypertonic solutions) also reveal no abnormalities. Expression of synaptotagmin-2, which lacks a seven amino acid sequence that contains the phosphorylation site in synaptotagmin-1, or a synaptotagmin-1 variant with these seven residues removed (Syt1(Δ109-116)), supports normal DAG-induced potentiation. These data suggest that this seven residue sequence in synaptotagmin-1 situated in the linker between the transmembrane and C2A domains is inhibitory in the unphosphorylated state and becomes permissive of potentiation upon phosphorylation. We conclude that synaptotagmin-1 phosphorylation is an essential step in PKC-dependent potentiation of synaptic transmission, acting downstream of the two other essential DAG/PKC substrates, Munc13-1 and Munc18-1.
Collapse
|
13
|
Calcium binding promotes conformational flexibility of the neuronal Ca(2+) sensor synaptotagmin. Biophys J 2016; 108:2507-2520. [PMID: 25992729 DOI: 10.1016/j.bpj.2015.04.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Revised: 04/07/2015] [Accepted: 04/09/2015] [Indexed: 01/12/2023] Open
Abstract
Synaptotagmin 1 (Syt1) is a synaptic vesicle protein that serves as a calcium sensor of neuronal secretion. It is established that calcium binding to Syt1 triggers vesicle fusion and release of neuronal transmitters, however, the dynamics of this process is not fully understood. To investigate how Ca(2+) binding affects Syt1 conformational dynamics, we performed prolonged molecular dynamics (MD) simulations of Ca(2+)-unbound and Ca(2+)-bound forms of Syt1. MD simulations were performed at a microsecond scale and combined with Monte Carlo sampling. We found that in the absence of Ca(2+) Syt1 structure in the solution is represented by an ensemble of conformational states with tightly coupled domains. To investigate the effect of Ca(2+) binding, we used two different strategies to generate a molecular model of a Ca(2+)-bound form of Syt1. First, we employed subsequent replacements of monovalent cations transiently captured within Syt1 Ca(2+)-binding pockets by Ca(2+) ions. Second, we performed MD simulations of Syt1 at elevated Ca(2+) levels. All the simulations produced Syt1 structures bound to four Ca(2+) ions, two ions chelated at the binding pocket of each domain. MD simulations of the Ca(2+)-bound form of Syt1 revealed that Syt1 conformational flexibility drastically increased upon Ca(2+) binding. In the presence of Ca(2+), the separation between domains increased, and interdomain rotations became more frequent. These findings suggest that Ca(2+) binding to Syt1 may induce major changes in the Syt1 conformational state, which in turn may initiate the fusion process.
Collapse
|
14
|
Zhou Q, Lai Y, Bacaj T, Zhao M, Lyubimov AY, Uervirojnangkoorn M, Zeldin OB, Brewster AS, Sauter NK, Cohen AE, Soltis SM, Alonso-Mori R, Chollet M, Lemke HT, Pfuetzner RA, Choi UB, Weis WI, Diao J, Südhof TC, Brunger AT. Architecture of the synaptotagmin-SNARE machinery for neuronal exocytosis. Nature 2015; 525:62-7. [PMID: 26280336 PMCID: PMC4607316 DOI: 10.1038/nature14975] [Citation(s) in RCA: 224] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Accepted: 07/27/2015] [Indexed: 02/07/2023]
Abstract
Synaptotagmin-1 and neuronal SNARE proteins have central roles in evoked synchronous neurotransmitter release; however, it is unknown how they cooperate to trigger synaptic vesicle fusion. Here we report atomic-resolution crystal structures of Ca(2+)- and Mg(2+)-bound complexes between synaptotagmin-1 and the neuronal SNARE complex, one of which was determined with diffraction data from an X-ray free-electron laser, leading to an atomic-resolution structure with accurate rotamer assignments for many side chains. The structures reveal several interfaces, including a large, specific, Ca(2+)-independent and conserved interface. Tests of this interface by mutagenesis suggest that it is essential for Ca(2+)-triggered neurotransmitter release in mouse hippocampal neuronal synapses and for Ca(2+)-triggered vesicle fusion in a reconstituted system. We propose that this interface forms before Ca(2+) triggering, moves en bloc as Ca(2+) influx promotes the interactions between synaptotagmin-1 and the plasma membrane, and consequently remodels the membrane to promote fusion, possibly in conjunction with other interfaces.
Collapse
Affiliation(s)
- Qiangjun Zhou
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Taulant Bacaj
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
| | - Minglei Zhao
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Artem Y Lyubimov
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Monarin Uervirojnangkoorn
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Oliver B Zeldin
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Aaron S Brewster
- Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Nicholas K Sauter
- Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Aina E Cohen
- SLAC National Accelerator Laboratory, Stanford, California 94305, USA
| | - S Michael Soltis
- SLAC National Accelerator Laboratory, Stanford, California 94305, USA
| | | | - Matthieu Chollet
- SLAC National Accelerator Laboratory, Stanford, California 94305, USA
| | - Henrik T Lemke
- SLAC National Accelerator Laboratory, Stanford, California 94305, USA
| | - Richard A Pfuetzner
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Ucheor B Choi
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - William I Weis
- Departments of Structural Biology, Molecular and Cellular Physiology, and Photon Science, Stanford University, Stanford, California 94305, USA
| | - Jiajie Diao
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| | - Thomas C Südhof
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
| | - Axel T Brunger
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
- Departments of Neurology and Neurological Sciences, Photon Science, and Structural Biology, Stanford University, Stanford, California 94305, USA
| |
Collapse
|
15
|
McAdam RL, Varga KT, Jiang Z, Young FB, Blandford V, McPherson PS, Gong LW, Sossin WS. The juxtamembrane region of synaptotagmin 1 interacts with dynamin 1 and regulates vesicle fission during compensatory endocytosis in endocrine cells. J Cell Sci 2015; 128:2229-35. [PMID: 25964652 DOI: 10.1242/jcs.161505] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Accepted: 04/30/2015] [Indexed: 12/25/2022] Open
Abstract
Synaptotagmin 1 (Syt1) is a synaptic vesicle protein that is important for the kinetics of both exocytosis and endocytosis, and is thus a candidate molecule to link these two processes. Although the tandem Ca(2+)-binding C2 domains of Syt1 have important roles in exocytosis and endocytosis, the function of the conserved juxtamembrane (jxm) linker region has yet to be determined. We now demonstrate that the jxm region of Syt1 interacts directly with the pleckstrin homology (PH) domain of the endocytic protein dynamin 1. By using cell-attached capacitance recordings with millisecond time resolution to monitor clathrin-mediated endocytosis of single vesicles in neuroendocrine chromaffin cells, we find that loss of this interaction prolongs the lifetime of the fission pore leading to defects in the dynamics of vesicle fission. These results indicate a previously undescribed interaction between two major regulatory proteins in the secretory vesicle cycle and that this interaction regulates endocytosis.
Collapse
Affiliation(s)
- Robyn L McAdam
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Kelly T Varga
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Zhongjiao Jiang
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Fiona B Young
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Vanessa Blandford
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Peter S McPherson
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| | - Liang-Wei Gong
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, USA
| | - Wayne S Sossin
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec, H3A 2B4, Canada
| |
Collapse
|
16
|
Kiessling V, Liang B, Tamm LK. Reconstituting SNARE-mediated membrane fusion at the single liposome level. Methods Cell Biol 2015; 128:339-63. [PMID: 25997356 DOI: 10.1016/bs.mcb.2015.02.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Successful reconstitutions of SNARE-mediated intracellular membrane fusion have been achieved in bulk fusion assays since 1998 and in single liposome fusion assays since 2004. Especially in neuronal presynaptic SNARE-mediated exocytosis, fusion is controlled by numerous accessory proteins, of which some functions have also been reconstituted in vitro. The development of and results obtained with two fundamentally different single liposome fusion assays, namely liposome-to-supported membrane and liposome-to-liposome, are reviewed. Both assays distinguish between liposome docking and fusion steps of the overall fusion reaction and both assays are capable of resolving hemi-and full-fusion intermediates and end states. They have opened new windows for elucidating the mechanisms of these fundamentally important cellular reactions with unprecedented time and molecular resolution. Although many of the molecular actors in this process have been discovered, we have only scratched the surface of looking at their fascinating plays, interactions, and choreographies that lead to vesicle traffic as well as neurotransmitter and hormone release in the cell.
Collapse
Affiliation(s)
- Volker Kiessling
- Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Binyong Liang
- Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Lukas K Tamm
- Center for Membrane Biology and Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| |
Collapse
|
17
|
Molecular origins of synaptotagmin 1 activities on vesicle docking and fusion pore opening. Sci Rep 2015; 5:9267. [PMID: 25791821 PMCID: PMC4366854 DOI: 10.1038/srep09267] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Accepted: 02/26/2015] [Indexed: 11/25/2022] Open
Abstract
Synaptotagmin 1 (Syt1), a major Ca2+ sensor in neuroexocytosis, utilizes SNARE- and membrane-binding to regulate vesicle fusion, a required process for neurotransmitter release at the synapse. However, the mechanism by which Syt1 orchestrates SNARE- and membrane- binding to control individual vesicle fusion steps is still unclear. In this study, we used a number of single vesicle assays that can differentiate intermediates of neuroexocytosis, to focus on Syt1 mutants that might impair Syt1-SNARE/PIP2 interaction, Ca2+-binding, or membrane penetration. Our results show that, although putative Syt1-SNARE/PIP2 coupling through the polybasic region of the C2B domain is critical for vesicle docking, its disruption does not affect content release. In contrast, Ca2+-binding and membrane-penetration mutants significantly reduce content release. Our results thus delineate multiple functions of Syt1 along the pathway of Ca2+-triggered exocytosis in unprecedented detail.
Collapse
|
18
|
Transmembrane tethering of synaptotagmin to synaptic vesicles controls multiple modes of neurotransmitter release. Proc Natl Acad Sci U S A 2015; 112:3793-8. [PMID: 25775572 DOI: 10.1073/pnas.1420312112] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synaptotagmin 1 (Syt1) is a synaptic vesicle integral membrane protein that regulates neurotransmitter release by activating fast synchronous fusion and suppressing slower asynchronous release. The cytoplasmic C2 domains of Syt1 interact with SNAREs and plasma membrane phospholipids in a Ca(2+)-dependent manner and can substitute for full-length Syt1 in in vitro membrane fusion assays. To determine whether synaptic vesicle tethering of Syt1 is required for normal fusion in vivo, we performed a structure-function study with tethering mutants at the Drosophila larval neuromuscular junction. Transgenic animals expressing only the cytoplasmic C2 domains or full-length Syt1 tethered to the plasma membrane failed to restore synchronous synaptic vesicle fusion, and also failed to clamp spontaneous vesicle release. In addition, transgenic animals with shorter, but not those with longer, linker regions separating the C2 domains from the transmembrane segment abolished Syt1's ability to activate synchronous vesicle fusion. Similar defects were observed when C2 domain alignment was altered to C2B-C2A from the normal C2A-C2B orientation, leaving the tether itself intact. Although cytoplasmic and plasma membrane-tethered Syt1 variants could not restore synchronous release in syt1 null mutants, they were very effective in promoting fusion through the slower asynchronous pathway. As such, the subcellular localization of Syt1 within synaptic terminals is important for the temporal dynamics that underlie synchronous and asynchronous neurotransmitter release.
Collapse
|
19
|
Lou X, Shin J, Yang Y, Kim J, Shin YK. Synaptotagmin-1 is an antagonist for Munc18-1 in SNARE zippering. J Biol Chem 2015; 290:10535-43. [PMID: 25716321 DOI: 10.1074/jbc.m114.631341] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Indexed: 12/17/2022] Open
Abstract
In neuroexocytosis, SNAREs and Munc18-1 may consist of the minimal membrane fusion machinery. Consistent with this notion, we observed, using single molecule fluorescence assays, that Munc18-1 stimulates SNARE zippering and SNARE-dependent lipid mixing in the absence of a major Ca(2+) sensor synaptotagmin-1 (Syt1), providing the structural basis for the conserved function of Sec1/Munc18 proteins in exocytosis. However, when full-length Syt1 is present, no enhancement of SNARE zippering and no acceleration of Ca(2+)-triggered content mixing by Munc18-1 are observed. Thus, our results show that Syt1 acts as an antagonist for Munc18-1 in SNARE zippering and fusion pore opening. Although the Sec1/Munc18 family may serve as part of the fusion machinery in other exocytotic pathways, Munc18-1 may have evolved to play a different role, such as regulating syntaxin-1a in neuroexocytosis.
Collapse
Affiliation(s)
- Xiaochu Lou
- From the Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011 and
| | - Jaeil Shin
- From the Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011 and
| | - Yoosoo Yang
- the Biomedical Research Institute, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 6, Seongbuk-gu, Seoul 136-791, South Korea
| | - Jaewook Kim
- the Biomedical Research Institute, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 6, Seongbuk-gu, Seoul 136-791, South Korea
| | - Yeon-Kyun Shin
- From the Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011 and the Biomedical Research Institute, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 6, Seongbuk-gu, Seoul 136-791, South Korea
| |
Collapse
|
20
|
Lin CC, Seikowski J, Pérez-Lara A, Jahn R, Höbartner C, Walla PJ. Control of membrane gaps by synaptotagmin-Ca2+ measured with a novel membrane distance ruler. Nat Commun 2014; 5:5859. [PMID: 25500905 PMCID: PMC4275583 DOI: 10.1038/ncomms6859] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 11/14/2014] [Indexed: 11/09/2022] Open
Abstract
Fast synchronous neurotransmitter release is triggered by calcium that activates synaptotagmin-1 (syt-1), resulting in fusion of synaptic vesicles with the presynaptic membrane. Syt-1 possesses two Ca(2+)-binding C2 domains that tether membranes via interactions with anionic phospholipids. It is capable of crosslinking membranes and has recently been speculated to trigger fusion by decreasing the gap between them. As quantitative information on membrane gaps is key to understanding general cellular mechanisms, including the role of syt-1, we developed a fluorescence-lifetime based inter-membrane distance ruler using membrane-anchored DNAs of various lengths as calibration standards. Wild-type and mutant data provide evidence that full-length syt-1 indeed regulates membrane gaps: without Ca(2+), syt-1 maintains membranes at distances of ~7-8 nm. Activation with 100 μM Ca(2+) decreases the distance to ~5 nm by binding the C2 domains to opposing membranes, respectively. These values reveal that activated syt-1 adjusts membrane distances to the level that promotes SNARE complex assembly.
Collapse
Affiliation(s)
- Chao-Chen Lin
- Research Group Biomolecular Spectroscopy and Single-Molecule Detection, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Jan Seikowski
- Research Group Nucleic Acid Chemistry, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Angel Pérez-Lara
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Reinhard Jahn
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany
| | - Claudia Höbartner
- 1] Research Group Nucleic Acid Chemistry, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany [2] Institute for Organic and Biomolecular Chemistry, Georg August University Göttingen, Tammannstraße 2, 37077 Göttingen, Germany
| | - Peter Jomo Walla
- 1] Research Group Biomolecular Spectroscopy and Single-Molecule Detection, Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany [2] Department of Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, University of Braunschweig, Hans-Sommer-Straße 10, 38106 Braunschweig, Germany
| |
Collapse
|
21
|
Lu B, Kiessling V, Tamm LK, Cafiso DS. The juxtamembrane linker of full-length synaptotagmin 1 controls oligomerization and calcium-dependent membrane binding. J Biol Chem 2014; 289:22161-71. [PMID: 24973220 DOI: 10.1074/jbc.m114.569327] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Synaptotagmin 1 (Syt1) is the calcium sensor for synchronous neurotransmitter release. The two C2 domains of Syt1, which may mediate fusion by bridging the vesicle and plasma membranes, are connected to the vesicle membrane by a 60-residue linker. Here, we use site-directed spin labeling and a novel total internal reflection fluorescence vesicle binding assay to characterize the juxtamembrane linker and to test the ability of reconstituted full-length Syt1 to interact with opposing membrane surfaces. EPR spectroscopy demonstrates that the majority of the linker interacts with the membrane interface, thereby limiting the extension of the C2A and C2B domains into the cytoplasm. Pulse dipolar EPR spectroscopy provides evidence that purified full-length Syt1 is oligomerized in the membrane, and mutagenesis indicates that a glycine zipper/GXXXG motif within the linker helps mediate oligomerization. The total internal reflection fluorescence-based vesicle binding assay demonstrates that full-length Syt1 that is reconstituted into supported lipid bilayers will capture vesicles containing negatively charged lipid in a Ca(2+)-dependent manner. Moreover, the rate of vesicle capture increases with Syt1 density, and mutations in the GXXXG motif that inhibit oligomerization of Syt1 reduce the rate of vesicle capture. This work demonstrates that modifications within the 60-residue linker modulate both the oligomerization of Syt1 and its ability to interact with opposing bilayers. In addition to controlling its activity, the oligomerization of Syt1 may play a role in organizing proteins within the active zone of membrane fusion.
Collapse
Affiliation(s)
- Bin Lu
- From the Departments of Chemistry and the Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22904
| | - Volker Kiessling
- the Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22904 Molecular Physiology and Biological Physics and
| | - Lukas K Tamm
- the Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22904 Molecular Physiology and Biological Physics and
| | - David S Cafiso
- From the Departments of Chemistry and the Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22904
| |
Collapse
|
22
|
Lai Y, Kim S, Varkey J, Lou X, Song JK, Diao J, Langen R, Shin YK. Nonaggregated α-synuclein influences SNARE-dependent vesicle docking via membrane binding. Biochemistry 2014; 53:3889-96. [PMID: 24884175 PMCID: PMC4075992 DOI: 10.1021/bi5002536] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
![]()
α-Synuclein
(α-Syn), a major component of Lewy body
that is considered as the hallmark of Parkinson’s disease (PD),
has been implicated in neuroexocytosis. Overexpression of α-Syn
decreases the neurotransmitter release. However, the mechanism by
which α-Syn buildup inhibits the neurotransmitter release is
still unclear. Here, we investigated the effect of nonaggregated α-Syn
on SNARE-dependent liposome fusion using fluorescence methods. In
ensemble in vitro assays, α-Syn reduces lipid mixing mediated
by SNAREs. Furthermore, with the more advanced single-vesicle assay
that can distinguish vesicle docking from fusion, we found that α-Syn
specifically inhibits vesicle docking, without interfering with the
fusion. The inhibition in vesicle docking requires α-Syn binding
to acidic lipid containing membranes. Thus, these results imply the
existence of at least two mechanisms of inhibition of SNARE-dependent
membrane fusion: at high concentrations, nonaggregated α-Syn
inhibits docking by binding acidic lipids but not v-SNARE; on the
other hand, at much lower concentrations, large α-Syn oligomers
inhibit via a mechanism that requires v-SNARE interaction [Choi et al. Proc. Natl. Acad. Sci.
U. S. A.2013, 110 (10), 4087−409223431141].
Collapse
Affiliation(s)
- Ying Lai
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University , Ames, Iowa 50011, United States
| | | | | | | | | | | | | | | |
Collapse
|