Munc18-1 binding to the neuronal SNARE complex controls synaptic vesicle priming

Deák, F.; Xu, Yi; Chang, Wen Pin; Dulubova, Irina; Khvotchev, Mikhail; Liu, Xinran; Südhof, Thomas C.; Rizo, Josep

doi:10.1083/jcb.200812026

Cited by 153 publications

(217 citation statements)

References 54 publications

(152 reference statements)

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“…It remains to be shown if this Ca 2ϩ -independent membrane fusion in the reconstituted in vitro assay, which only uses a limited number of purified components, reflects some shortcoming of the assay or potentially reproduces spontaneous vesicle fusion in vivo. Interestingly, Munc18-1 stimulates both spontaneous and evoked release in neurons, consistent with our in vitro data (64).…”

Section: Discussionsupporting

confidence: 81%

“…In the presence of Syt1, Munc18-1 not only dramatically increases the initial fusion rate but also the final extent of membrane fusion, consistent with its SNAREpin assembly function. Thus, the majority of the vesicles docked by Syt1 are efficiently shifted into a reactive pool, which would be consistent with studies in living cells that demonstrated that Munc18-1 can regulate the size of the readily releasable pool of vesicles (63,64). Interestingly, recent in vitro reconstitution experiments showed that Syt1 docks vesicles, but a considerable time passes before these vesicles can fuse (28).…”

Section: Discussionsupporting

confidence: 67%

“…While Munc18-1 targets the C-terminal part of VAMP2, CpxII is directed toward the assembled N-terminal part of the partially assembled SNAREpin. Indeed, it has been shown that both complexin and Munc18-1 can simultaneously bind SNARE complexes (64). An already available structure of a complexin-SNAREpin mimetic demonstrates that complexin binds via its central helix in an anti-parallel manner to the N-terminal end of partially assembled SNAREpins (21).…”

Section: Discussionmentioning

confidence: 99%

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SNAREpin Assembly by Munc18-1 Requires Previous Vesicle Docking by Synaptotagmin 1

Parisotto

Malsam

Scheutzow

et al. 2012

Journal of Biological Chemistry

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Background:The cascade of reactions and proteins conferring regulated exocytosis needs to be characterized. Results: Synaptotagmin 1 is a primary vesicle-docking factor, and Munc18-1 accelerates subsequent v-/t-SNARE assembly/zippering. Conclusion: Synaptotagmin 1, PI(4,5)P 2 , complexin II, and Munc18-1 function in a sequential and concerted manner to mediate vesicle docking, SNAREpin assembly, and fast Ca 2ϩ -triggered exocytosis. Significance: Efficient Ca 2ϩ -regulated membrane fusion was reconstituted from a minimal set of components.

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Section: Discussionsupporting

confidence: 81%

Section: Discussionsupporting

confidence: 67%

Section: Discussionmentioning

confidence: 99%

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SNAREpin Assembly by Munc18-1 Requires Previous Vesicle Docking by Synaptotagmin 1

Parisotto

Malsam

Scheutzow

et al. 2012

Journal of Biological Chemistry

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“…We used isothermal titration calorimetry (ITC) to evaluate the binding of Munc18 proteins to cognate Sxs with and without the N-peptide. The Munc18-1 results recapitulate those of others (14,28,32) showing that Sx1a and Sx1a lacking its N-peptide (Sx1aΔN) bind to Munc18-1 with similar high affinities (K d , 1.4 and 10 nM, respectively; see Table S1 for full details).…”

Section: Resultssupporting

confidence: 65%

Low-resolution solution structures of Munc18:Syntaxin protein complexes indicate an open binding mode driven by the Syntaxin N-peptide

Christie¹,

Whitten²,

King³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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When nerve cells communicate, vesicles from one neuron fuse with the presynaptic membrane releasing chemicals that signal to the next. Similarly, when insulin binds its receptor on adipocytes or muscle, glucose transporter-4 vesicles fuse with the cell membrane, allowing glucose to be imported. These essential processes require the interaction of SNARE proteins on vesicle and cell membranes, as well as the enigmatic protein Munc18 that binds the SNARE protein Syntaxin. Here, we show that in solution the neuronal protein Syntaxin1a interacts with Munc18-1 whether or not the Syntaxin1a N-peptide is present. Conversely, the adipocyte protein Syntaxin4 does not bind its partner Munc18c unless the N-peptide is present. Solution-scattering data for the Munc18-1:Syntaxin1a complex in the absence of the N-peptide indicates that this complex adopts the inhibitory closed binding mode, exemplified by a crystal structure of the complex. However, when the N-peptide is present, the solution-scattering data indicate both Syntaxin1a and Syntaxin4 adopt extended conformations in complexes with their respective Munc18 partners. The low-resolution solution structure of the open Munc18:Syntaxin binding mode was modeled using data from cross-linking/mass spectrometry, small-angle X-ray scattering, and small-angle neutron scattering with contrast variation, indicating significant differences in Munc18:Syntaxin interactions compared with the closed binding mode. Overall, our results indicate that the neuronal Munc18-1:Syntaxin1a proteins can adopt two alternate and functionally distinct binding modes, closed and open, depending on the presence of the N-peptide, whereas Munc18c:Syntaxin4 adopts only the open binding mode. membrane fusion | protein interactions | small-angle neutron scattering | small-angle X-ray scattering M embrane trafficking is an essential and highly regulated process whereby cargo-carrying vesicles are directed to dock and fuse with specific cell membranes. The process requires soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins on vesicle and target membranes. These interact to form high-affinity SNARE complexes required for docking and membrane fusion (1, 2). Structurally, the SNARE complex is a parallel four-helix bundle comprising helices contributed from several partner SNAREs (3). This helical bundle promotes vesicle fusion by bringing the vesicle and plasma membranes into close proximity and by providing the energy required for membrane fusion (4, 5).In the neuronal synapse, neurotransmitters are released from nerve cells by SNARE-mediated fusion of vesicles with the plasma membrane in response to action potentials. In this process, one of four SNARE helices is contributed by Syntaxin (Sx) 1a, a protein localized at the plasma membrane by a transmembrane helix. In addition to its membrane-anchored SNARE helix (H3), Sx1a has an Habc domain that can bind to the H3 helix (6) forming a closed Sx1a conformation (Fig. 1A). This closed conformation inactivates Sx1a by preventing H3 inter...

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“…We found that Munc18c bound to the soluble form of the ternary SNARE complex with a K d of ∼1 μM (Fig. 1B), similar to the association of Munc18-1 with soluble synaptic SNARE complexes (34,52). ITC measurements showed that Munc18c bound to the SNARE complex at a ratio close to 1:1 (Fig.…”

Section: Resultsmentioning

confidence: 75%

Comparative studies of Munc18c and Munc18-1 reveal conserved and divergent mechanisms of Sec1/Munc18 proteins

Rathore

Lopez

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

154

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Sec1/Munc18 (SM) family proteins are essential for every vesicle fusion pathway. The best-characterized SM protein is the synaptic factor Munc18-1, but it remains unclear whether its functions represent conserved mechanisms of SM proteins or specialized activities in neurotransmitter release. To address this question, we dissected Munc18c, a functionally distinct SM protein involved in nonsynaptic exocytic pathways. We discovered that Munc18c binds to the trans-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex and strongly accelerates the fusion rate. Further analysis suggests that Munc18c recognizes both vesicle-rooted SNARE and target membrane-associated SNAREs, and promotes trans-SNARE zippering at the postdocking stage of the fusion reaction. The stimulation of fusion by Munc18c is specific to its cognate SNARE isoforms. Because Munc18-1 regulates fusion in a similar manner, we conclude that one conserved function of SM proteins is to bind their cognate trans-SNARE complexes and accelerate fusion kinetics. Munc18c also binds syntaxin-4 monomer but does not block target membrane-associated SNARE assembly, in agreement with our observation that six-to eightfold increases in Munc18c expression do not inhibit insulinstimulated glucose uptake in adipocytes. Thus, the inhibitory "closed" syntaxin binding mode demonstrated for Munc18-1 is not conserved in Munc18c. Unexpectedly, we found that Munc18c recognizes the N-terminal region of the vesicle-rooted SNARE, whereas Munc18-1 requires the C-terminal sequences, suggesting that the architecture of the SNARE/SM complex likely differs across fusion pathways. Together, these comparative studies of two distinct SM proteins reveal conserved as well as divergent mechanisms of SM family proteins in intracellular vesicle fusion. membrane fusion | vesicle transport | exocytosis T he fusion of intracellular vesicles with target membranes requires two classes of conserved proteins: SNAREs and SM (Sec1/Munc18) proteins (1, 2). SNAREs are membrane-associated proteins that contain characteristic stretches of 60-70 amino acids known as core domains or SNARE motifs. Fusion is initiated when the core domains of the vesicle-rooted SNARE (v-SNARE) and the target membrane-associated SNAREs (t-SNAREs) zipper into a four-helix trans-SNARE complex between two apposed bilayers (2-5). N-to C-terminal zippering of the trans-SNARE complex brings the two membranes into close apposition to fuse (6-8).First isolated in genetic screens in yeast and nematodes (9, 10), SM proteins are hydrophilic factors of 60-70 kDa that regulate membrane fusion through binding to their cognate SNAREs (11-13). SM proteins exhibit a similar loss-of-function phenotype as that of SNAREs (i.e., abrogation of fusion) and are essential for every pathway of intracellular vesicle fusion (14-16). Mutations of SM proteins give rise to a number of human diseases, including epilepsy and inflammatory disorders, as well as arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome (17-...

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Munc18-1 binding to the neuronal SNARE complex controls synaptic vesicle priming

Cited by 153 publications

References 54 publications

SNAREpin Assembly by Munc18-1 Requires Previous Vesicle Docking by Synaptotagmin 1

SNAREpin Assembly by Munc18-1 Requires Previous Vesicle Docking by Synaptotagmin 1

Low-resolution solution structures of Munc18:Syntaxin protein complexes indicate an open binding mode driven by the Syntaxin N-peptide

Comparative studies of Munc18c and Munc18-1 reveal conserved and divergent mechanisms of Sec1/Munc18 proteins

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