151
|
Lisman JE, Raghavachari S, Tsien RW. The sequence of events that underlie quantal transmission at central glutamatergic synapses. Nat Rev Neurosci 2007; 8:597-609. [PMID: 17637801 DOI: 10.1038/nrn2191] [Citation(s) in RCA: 171] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The properties of synaptic transmission were first elucidated at the neuromuscular junction. More recent work has examined transmission at synapses within the brain. Here we review the remarkable progress in understanding the biophysical and molecular basis of the sequential steps in this process. These steps include the elevation of Ca2+ in microdomains of the presynaptic terminal, the diffusion of transmitter through the fusion pore into the synaptic cleft and the activation of postsynaptic receptors. The results give insight into the factors that control the precision of quantal transmission and provide a framework for understanding synaptic plasticity.
Collapse
Affiliation(s)
- John E Lisman
- Brandeis University, Department of Biology, MS 008, 415 South Street, Waltham, Massachusetts 02454-9110, USA.
| | | | | |
Collapse
|
152
|
Zhao L, Burkin HR, Shi X, Li L, Reim K, Miller DJ. Complexin I is required for mammalian sperm acrosomal exocytosis. Dev Biol 2007; 309:236-44. [PMID: 17692307 PMCID: PMC2099451 DOI: 10.1016/j.ydbio.2007.07.009] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Revised: 07/10/2007] [Accepted: 07/12/2007] [Indexed: 12/17/2022]
Abstract
Regulated exocytosis in many cells is controlled by the SNARE complex, whose core includes three proteins that promote membrane fusion. Complexins I and II are highly related cytosolic proteins that bind tightly to the assembled SNARE complex and regulate neuronal exocytosis. Like somatic cells, sperm undergo regulated exocytosis; however, sperm release a single large vesicle, the acrosome, whose release has different characteristics than neuronal exocytosis. Acrosomal release is triggered upon sperm adhesion to the mammalian egg extracellular matrix (zona pellucida) to allow penetration of the egg coat. Membrane fusion occurs at multiple points within the acrosome but how fusion is activated and the formation and progression of fusion points is synchronized is unclear. We show that complexins I and II are found in acrosome-intact mature sperm, bind to SNARE complex proteins, and are not detected in sperm after acrosomal exocytosis (acrosome reaction). Although complexin-I-deficient sperm acrosome-react in response to calcium ionophore, they do not acrosome-react in response to egg zona pellucida proteins and have reduced fertilizing ability, in vitro. Complexin II is present in the complexin-I-deficient sperm and its expression is increased in complexin-I-deficient testes. Therefore, complexin I functions in exocytosis in two related but morphologically distinct secretory processes. Sperm are unusual because they express both complexins I and II but have a unique and specific requirement for complexin I.
Collapse
Affiliation(s)
- Longmei Zhao
- University of Illinois, Department of Animal Sciences, 1207 West Gregory Drive, Urbana, Illinois 61801
| | - Heather R. Burkin
- University of Illinois, Department of Animal Sciences, 1207 West Gregory Drive, Urbana, Illinois 61801
| | - Xudong Shi
- University of Illinois, Department of Animal Sciences, 1207 West Gregory Drive, Urbana, Illinois 61801
| | - Lingjun Li
- University of Wisconsin, School of Pharmacy, 777 Highland Avenue, Madison, Wisconsin 53705
| | - Kerstin Reim
- Max-Plank-Institute for Experimental Medicine, Department of Molecular Neurobiology, D-37075 Göttingen, Germany
| | - David J. Miller
- University of Illinois, Department of Animal Sciences, 1207 West Gregory Drive, Urbana, Illinois 61801
- Correspondence should be addressed to: David J. Miller, University of Illinois, 1207 West Gregory Drive, Urbana, Illinois 61801, Tel: (217) 333-3408, Fax: (217) 333-8286, e-mail:
| |
Collapse
|
153
|
Roggero CM, De Blas GA, Dai H, Tomes CN, Rizo J, Mayorga LS. Complexin/synaptotagmin interplay controls acrosomal exocytosis. J Biol Chem 2007; 282:26335-43. [PMID: 17613520 DOI: 10.1074/jbc.m700854200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulated secretion is a fundamental process underlying the function of many cell types. In particular, acrosomal exocytosis in mammalian sperm is essential for egg fertilization. Regulated secretion requires SNARE proteins and, in neurons, also synaptotagmin I and complexin. Recent reports suggest that complexin imposes a fusion block that is released by Ca(2+) and synaptotagmin I. However, no direct evidence for this model in secreting cells has been provided and whether this complexin/synaptotagmin interplay functions in other types of secretion is unknown. In this report, we show that the C2B domain of synaptotagmin VI and an anti-complexin antibody blocked the formation of trans SNARE complexes in permeabilized human sperm, and that this effect was reversed by adding complexin. In contrast, an excess of complexin stopped exocytosis at a later step, when SNAREs were assembled in loose trans complexes. Interestingly, this blockage was released by the addition of the synaptotagmin VI C2B domain in the presence of Ca(2+). We have previously demonstrated that the activity of this domain is regulated by protein kinase C-mediated phosphorylation. Here, we show that a phosphomimetic mutation in the polybasic region of the C2B domain strongly affects its Ca(2+) and phospholipids binding properties. Importantly, this mutation completely abrogates its ability to rescue the complexin block. Our results show that the functional interplay between complexin and synaptotagmin has a central role in a physiological secretion event, and that this interplay can be modulated by phosphorylation of the C2B domain.
Collapse
Affiliation(s)
- Carlos M Roggero
- Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología (IHEM-CONICET), Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, Mendoza 5500, Argentina
| | | | | | | | | | | |
Collapse
|
154
|
Wojcik SM, Brose N. Regulation of Membrane Fusion in Synaptic Excitation-Secretion Coupling: Speed and Accuracy Matter. Neuron 2007; 55:11-24. [PMID: 17610814 DOI: 10.1016/j.neuron.2007.06.013] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Unlike most other secretory processes, neurotransmitter release at chemical synapses is extremely fast, tightly regulated, spatially restricted, and dynamically adjustable at the same time. In this review, we focus on recent discoveries of molecular and cell biological processes that determine how fusion competence of vesicles is achieved and controlled in order to suit the specific requirements of synaptic transmitter release with respect to speed and spatial selectivity.
Collapse
Affiliation(s)
- Sonja M Wojcik
- Max-Planck-Institut für Experimentelle Medizin, Abteilung Molekulare Neurobiologie, Hermann-Rein-Strasse 3, D-37075 Göttingen, Deutschland.
| | | |
Collapse
|
155
|
Li Y, Augustine GJ, Weninger K. Kinetics of complexin binding to the SNARE complex: correcting single molecule FRET measurements for hidden events. Biophys J 2007; 93:2178-87. [PMID: 17513363 PMCID: PMC1959531 DOI: 10.1529/biophysj.106.101220] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Virtually all measurements of biochemical kinetics have been derived from macroscopic measurements. Single-molecule methods can reveal the kinetic behavior of individual molecular complexes and thus have the potential to determine heterogeneous behaviors. Here we have used single-molecule fluorescence resonance energy transfer to determine the kinetics of binding of SNARE (soluble N-ethyl maleimide-sensitive fusion protein attachment protein receptor) complexes to complexin and to a peptide derived from the central SNARE binding region of complexin. A Markov model was developed to account for the presence of unlabeled competitor in such measurements. We find that complexin associates rapidly with SNARE complexes anchored in lipid bilayers with a rate constant of 7.0 x 10(6) M(-1) s(-1) and dissociates slowly with a rate constant of 0.3 s(-1). The complexin peptide associates with SNARE complexes at a rate slower than that of full-length complexin (1.2 x 10(6) M(-1) s(-1)), and dissociates much more rapidly (rate constant >67 s(-1)). Comparison of single-molecule fluorescence resonance energy transfer measurements made using several dye attachment sites illustrates that dye labeling of complexin can modify its rate of unbinding from SNAREs. These rate constants provide a quantitative framework for modeling of the cascade of reactions underlying exocytosis. In addition, our theoretical correction establishes a general approach for improving single-molecule measurements of intermolecular binding kinetics.
Collapse
Affiliation(s)
- Yulong Li
- Department of Neurobiology, Duke University Medical Center, Durham, NC, USA
| | | | | |
Collapse
|
156
|
Collins KM, Wickner WT. Trans-SNARE complex assembly and yeast vacuole membrane fusion. Proc Natl Acad Sci U S A 2007; 104:8755-60. [PMID: 17502611 PMCID: PMC1885575 DOI: 10.1073/pnas.0702290104] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
cis-SNARE complexes (anchored in one membrane) are disassembled by Sec17p (alpha-SNAP) and Sec18p (NSF), permitting the unpaired SNAREs to assemble in trans. We now report a direct assay of trans-SNARE complex formation during yeast vacuole docking. SNARE complex assembly and fusion is promoted by high concentrations of the SNARE Vam7p or Nyv1p or by addition of HOPS (homotypic fusion and vacuole protein sorting), a Ypt7p (Rab)-effector complex with a Sec1/Munc18-family subunit. Inhibitors that target Ypt7p, HOPS, or key regulatory lipids prevent trans-SNARE complex assembly and ensuing fusion. Strikingly, the lipid ligand MED (myristoylated alanine-rich C kinase substrate effector domain) or elevated concentrations of Sec17p, which can displace HOPS from SNARE complexes, permit full trans-SNARE pairing but block fusion. These findings suggest that efficient fusion requires trans-SNARE complex associations with factors such as HOPS and subsequent regulated lipid rearrangements.
Collapse
Affiliation(s)
- Kevin M. Collins
- Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755-3844
| | - William T. Wickner
- Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755-3844
- To whom correspondence should be addressed. E-mail:
| |
Collapse
|
157
|
Zink M, Vollmayr B, Gebicke-Haerter PJ, Henn FA, Thome J. Reduced expression of complexins I and II in rats bred for learned helplessness. Brain Res 2007; 1144:202-8. [PMID: 17320830 DOI: 10.1016/j.brainres.2007.01.066] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Revised: 11/29/2006] [Accepted: 01/23/2007] [Indexed: 10/23/2022]
Abstract
Disturbed synaptic transmission contributes to the pathophysiology of mood disorders. Post mortem studies reported reduced expression of the synaptic vesicle protein (SVP) complexins I and II in depression. Antidepressants were found to induce the expression of these genes. Since animals with congenital susceptibility to learned helplessness provide a valid animal model of depression, we investigated the expression of different SVPs in this system by semiquantitative in situ hybridization. Rats bred for congenital learned helpless behavior (cLH, N=6) failed to interrupt foot shock currents by lever pressing (mean 12.3 failures out of 15 trials). These animals showed significantly lower expression of complexins I and II mRNA in hippocampal, limbic and cortical brain areas compared to not helpless animals (cNLH, N=6) with a mean failure rate of 0.83 out of 15 trials. Expression levels of complexins I and II significantly correlated with the failure rate in the test paradigm. In contrast, the expressions of synaptotagmin I and synaptophysin were found unchanged. This investigation provides a further validation of the LH model of depression. The experimental data fit well into current pathogenetic concepts of mood disorders and support the hypothesis, that complexins are pivotal players in the pathophysiology of depression and tentative targets of antidepressants.
Collapse
Affiliation(s)
- Mathias Zink
- Central Institute of Mental Health, Department of Psychiatry and Psychotherapy, PO Box: 12 21 20, D-68072 Mannheim, Germany.
| | | | | | | | | |
Collapse
|
158
|
Liu J, Guo T, Wu J, Bai X, Zhou Q, Sui SF. Overexpression of complexin in PC12 cells inhibits exocytosis by preventing SNARE complex recycling. BIOCHEMISTRY (MOSCOW) 2007; 72:439-44. [PMID: 17511609 DOI: 10.1134/s0006297907040116] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Complexin is an important protein that functions during Ca2+-dependent neurotransmitter release. Substantial evidence supports that complexin performs its role through rapid interaction with SNARE complex with high affinity. However, alpha-SNAP/NSF, which can disassemble the cis-SNARE complex in the presence of MgATP, competes with complexin to bind to SNARE complex. In addition, injection of alpha-SNAP into chromaffin cells enhances the size of the readily releasable pool, and mutation disrupting the ATPase activity of NSF results in the accumulation of SNARE complex. Thus, whether high concentrations of complexin could result in a reverse result is unclear. In this paper, we demonstrate that when stably overexpressed in PC12 cells, high levels of complexin result in the accumulation of SNARE complex. This in turn leads to a reduction in the size of the readily releasable pool of large dense core vesicles. These results suggest that high levels of complexin seem to prevent SNARE complex recycling, presumably by displacing NSF and alpha-SNAP from SNARE complex.
Collapse
Affiliation(s)
- Jingguo Liu
- Department of Biological Sciences and Biotechnology, State-Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China
| | | | | | | | | | | |
Collapse
|
159
|
Melia TJ. Putting the clamps on membrane fusion: How complexin sets the stage for calcium-mediated exocytosis. FEBS Lett 2007; 581:2131-9. [PMID: 17350005 DOI: 10.1016/j.febslet.2007.02.066] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2007] [Revised: 02/15/2007] [Accepted: 02/26/2007] [Indexed: 11/20/2022]
Abstract
Three recent papers have addressed a long-standing question in exocytosis: how does a sudden calcium influx trigger a coordinated synchronous release in regulated exocytosis [Giraudo, C.G., Eng, W.S., Melia, T.J. and Rothman, J.E. (2006) A clamping mechanism involved in SNARE-dependent exocytosis. Science 313, 676-680; Schaub, J.R., Lu, X., Doneske, B., Shin, Y.K. and McNew, J.A. (2006) Hemifusion arrest by complexin is relieved by Ca(2+)-synaptotagmin I. Nat. Struct. Mol. Biol. 13, 748-750; Tang, J., Maximov, A., Shin, O.H., Dai, H., Rizo, J. and Sudhof, T.C. (2006) A complexin/synaptotagmin 1 switch controls fast synaptic vesicle exocytosis. Cell 126, 1175-1187]? Using diverse approaches that include cell-free reconstitution of the membrane fusion machinery and in vivo manipulation of fusogenic proteins, these groups have established that the complexin proteins are fusion clamps. By arresting vesicle secretion just prior to fusion, complexin primes select vesicles for a fast, synchronous response to calcium.
Collapse
Affiliation(s)
- Thomas J Melia
- Columbia University, Department of Physiology and Cellular Biophysics, 1150 Saint Nicholas Avenue, New York, NY 10032, USA
| |
Collapse
|
160
|
Dai H, Shen N, Araç D, Rizo J. A quaternary SNARE-synaptotagmin-Ca2+-phospholipid complex in neurotransmitter release. J Mol Biol 2007; 367:848-63. [PMID: 17320903 PMCID: PMC1855161 DOI: 10.1016/j.jmb.2007.01.040] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2006] [Revised: 01/08/2007] [Accepted: 01/16/2007] [Indexed: 10/23/2022]
Abstract
The function of synaptotagmin as a Ca(2+) sensor in neurotransmitter release involves Ca(2+)-dependent phospholipid binding to its two C(2) domains, but this activity alone does not explain why Ca(2+) binding to the C(2)B domain is more critical for release than Ca(2+) binding to the C(2)A domain. Synaptotagmin also binds to SNARE complexes, which are central components of the membrane fusion machinery, and displaces complexins from the SNAREs. However, it is unclear how phospholipid binding to synaptotagmin is coupled to SNARE binding and complexin displacement. Using supported lipid bilayers deposited within microfluidic channels, we now show that Ca(2+) induces simultaneous binding of synaptotagmin to phospholipid membranes and SNARE complexes, resulting in an intimate quaternary complex that we name SSCAP complex. Mutagenesis experiments show that Ca(2+) binding to the C(2)B domain is critical for SSCAP complex formation and displacement of complexin, providing a clear rationale for the preponderant role of the C(2)B domain in release. This and other correlations between the effects of mutations on SSCAP complex formation and their functional effects in vivo suggest a key role for this complex in release. We propose a model whereby the highly positive electrostatic potential at the tip of the SSCAP complex helps to induce membrane fusion during release.
Collapse
Affiliation(s)
- Han Dai
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390
- Department of Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390
| | - Nan Shen
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138
| | - Demet Araç
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390
- Department of Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390
| | - Josep Rizo
- Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390
- Department of Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390
- * Correspondence: ; phone: 214-645-6360; FAX: 214-645-6353
| |
Collapse
|
161
|
Shata A, Saisu H, Odani S, Abe T. Phosphorylated synaphin/complexin found in the brain exhibits enhanced SNARE complex binding. Biochem Biophys Res Commun 2007; 354:808-13. [PMID: 17266930 DOI: 10.1016/j.bbrc.2007.01.064] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Accepted: 01/13/2007] [Indexed: 11/20/2022]
Abstract
The cytosolic protein synaphin/complexin critically regulates fast neurotransmitter release at the synapse by binding to SNARE complex. However, the exact mechanism of its action remains unclear, and very little is known about how it is physiologically regulated. Here we show that synaphins (Syps) 1 and 2 can be phosphorylated in vitro by protein kinase CK2 (CK2). The only phosphorylation site by CK2 was serine-115 (Ser-115) of Syps 1 and 2. Syps 1 and 2 exhibited higher affinities to native and recombinant SNARE complexes when phosphorylated at Ser-115. We found Ser-115-phosphorylated Syp 1 (pS115-Syp 1) in the cytosolic fraction of the rat brain using polyclonal antibody specific to pS115-Syps 1 and 2. These results suggest that the activity of Syp is regulated by CK2 phosphorylation of its Ser-115 in vivo. The phosphorylation may provide a new route for modulating fast neurotransmitter release.
Collapse
Affiliation(s)
- Atsushi Shata
- Department of Cellular Neurobiology, Brain Research Institute, Niigata University, Niigata 951-8585, Japan
| | | | | | | |
Collapse
|
162
|
Shen J, Tareste DC, Paumet F, Rothman JE, Melia TJ. Selective Activation of Cognate SNAREpins by Sec1/Munc18 Proteins. Cell 2007; 128:183-95. [PMID: 17218264 DOI: 10.1016/j.cell.2006.12.016] [Citation(s) in RCA: 365] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2006] [Revised: 10/31/2006] [Accepted: 12/05/2006] [Indexed: 01/11/2023]
Abstract
Sec1/Munc18 (SM) proteins are required for every step of intracellular membrane fusion, but their molecular mechanism of action has been unclear. In this work, we demonstrate a fundamental role of the SM protein: to act as a stimulatory subunit of its cognate SNARE fusion machinery. In a reconstituted system, mammalian SNARE pairs assemble between bilayers to drive a basal fusion reaction. Munc18-1/nSec1, a synaptic SM protein required for neurotransmitter release, strongly accelerates this reaction through direct contact with both t- and v-SNAREs. Munc18-1 accelerates fusion only for the cognate SNAREs for exocytosis, therefore enhancing fusion specificity.
Collapse
Affiliation(s)
- Jingshi Shen
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY 10032, USA
| | | | | | | | | |
Collapse
|
163
|
Yoon TY, Okumus B, Zhang F, Shin YK, Ha T. Multiple intermediates in SNARE-induced membrane fusion. Proc Natl Acad Sci U S A 2006; 103:19731-6. [PMID: 17167056 PMCID: PMC1698870 DOI: 10.1073/pnas.0606032103] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Membrane fusion in eukaryotic cells is thought to be mediated by a highly conserved family of proteins called SNAREs (soluble N-ethyl maleimide sensitive-factor attachment protein receptors). The vesicle-associated v-SNARE engages with its partner t-SNAREs on the target membrane to form a coiled coil that bridges two membranes and facilitates fusion. As demonstrated by recent findings on the hemifusion state, identifying intermediates of membrane fusion can help unveil the underlying fusion mechanism. Observation of SNARE-driven fusion at the single-liposome level has the potential to dissect and characterize fusion intermediates most directly. Here, we report on the real-time observation of lipid-mixing dynamics in a single fusion event between a pair of SNARE-reconstituted liposomes. The assay reveals multiple intermediate states characterized by discrete values of FRET between membrane-bound fluorophores. Hemifusion, flickering of fusion pores, and kinetic transitions between intermediates, which would be very difficult to detect in ensemble assays, are now identified. The ability to monitor the time course of fusion events between two proteoliposomes should be useful for addressing many important issues in SNARE-mediated membrane fusion.
Collapse
Affiliation(s)
| | - Burak Okumus
- Center for Biophysics and Computational Biology, and
| | - Fan Zhang
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011
| | - Yeon-Kyun Shin
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011
- To whom correspondence may be addressed. E-mail:
or
| | - Taekjip Ha
- *Howard Hughes Medical Institute
- Center for Biophysics and Computational Biology, and
- Department of Physics, University of Illinois at Urbana–Champaign, Urbana, IL 61801; and
- To whom correspondence may be addressed. E-mail:
or
| |
Collapse
|
164
|
Tang J, Maximov A, Shin OH, Dai H, Rizo J, Südhof TC. A complexin/synaptotagmin 1 switch controls fast synaptic vesicle exocytosis. Cell 2006; 126:1175-87. [PMID: 16990140 DOI: 10.1016/j.cell.2006.08.030] [Citation(s) in RCA: 329] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2006] [Revised: 06/29/2006] [Accepted: 08/18/2006] [Indexed: 10/24/2022]
Abstract
Ca(2+) binding to synaptotagmin 1 triggers fast exocytosis of synaptic vesicles that have been primed for release by SNARE-complex assembly. Besides synaptotagmin 1, fast Ca(2+)-triggered exocytosis requires complexins. Synaptotagmin 1 and complexins both bind to assembled SNARE complexes, but it is unclear how their functions are coupled. Here we propose that complexin binding activates SNARE complexes into a metastable state and that Ca(2+) binding to synaptotagmin 1 triggers fast exocytosis by displacing complexin from metastable SNARE complexes. Specifically, we demonstrate that, biochemically, synaptotagmin 1 competes with complexin for SNARE-complex binding, thereby dislodging complexin from SNARE complexes in a Ca(2+)-dependent manner. Physiologically, increasing the local concentration of complexin selectively impairs fast Ca(2+)-triggered exocytosis but retains other forms of SNARE-dependent fusion. The hypothesis that Ca(2+)-induced displacement of complexins from SNARE complexes triggers fast exocytosis accounts for the loss-of-function and gain-of-function phenotypes of complexins and provides a molecular explanation for the high speed and synchronicity of fast Ca(2+)-triggered neurotransmitter release.
Collapse
Affiliation(s)
- Jiong Tang
- The Center for Basic Neuroscience, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | | | | | | | | | | |
Collapse
|
165
|
Chernomordik LV, Zimmerberg J, Kozlov MM. Membranes of the world unite! J Cell Biol 2006; 175:201-7. [PMID: 17043140 PMCID: PMC2064561 DOI: 10.1083/jcb.200607083] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2006] [Accepted: 09/08/2006] [Indexed: 11/22/2022] Open
Abstract
Despite diverse origins, cellular fusion mechanisms converge at a pathway of phospholipid bilayer fusion. In this mini-review, we discuss how proteins can mediate each of the three major stages in the fusion pathway: contact, hemifusion, and the opening of an expanding fusion pore.
Collapse
Affiliation(s)
- Leonid V Chernomordik
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
| | | | | |
Collapse
|