The role of non-canonical SNAREs in synaptic vesicle recycling

Ramirez, Denise M.O.; Kavalali, Ege T.

doi:10.4161/cl.20114

Cited by 27 publications

(23 citation statements)

References 96 publications

(155 reference statements)

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“…This conclusion is consistent with additional studies examining the contribution of the Cpx C terminus in regulating synaptic vesicle release (17,(31)(32)(33)36). What mechanism is ultimately used to separate Cpx's role in spontaneous vs. evoked release is still unclear, and may involve a complex interplay with the SNARE complex and other SNARE-associated proteins, including Syt (37,38). These distinct roles may also be manifest through effects of Cpx on molecularly distinct pools of vesicles (39), or on specific active zones dedicated to evoked vs. spontaneous release (40).…”

Section: Discussionsupporting

confidence: 77%

Genetic analysis of the Complexin trans-clamping model for cross-linking SNARE complexes in vivo

Cho

Kümmel

et al. 2014

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

102

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Complexin (Cpx) is a SNARE-binding protein that regulates neurotransmission by clamping spontaneous synaptic vesicle fusion in the absence of Ca 2+ influx while promoting evoked release in response to an action potential. Previous studies indicated Cpx may cross-link multiple SNARE complexes via a trans interaction to function as a fusion clamp. During Ca 2+ influx, Cpx is predicted to undergo a conformational switch and collapse onto a single SNARE complex in a cis-binding mode to activate vesicle release. To test this model in vivo, we performed structure-function studies of the Cpx protein in Drosophila. Using genetic rescue approaches with cpx mutants that disrupt SNARE cross-linking, we find that manipulations that are predicted to block formation of the trans SNARE array disrupt the clamping function of Cpx. Unexpectedly, these same mutants rescue action potential-triggered release, indicating trans-SNARE cross-linking by Cpx is not a prerequisite for triggering evoked fusion. In contrast, mutations that impair Cpxmediated cis-SNARE interactions that are necessary for transition from an open to closed conformation fail to rescue evoked release defects in cpx mutants, although they clamp spontaneous release normally. Our in vivo genetic manipulations support several predictions made by the Cpx cross-linking model, but unexpected results suggest additional mechanisms are likely to exist that regulate Cpx's effects on SNARE-mediated fusion. Our findings also indicate that the inhibitory and activating functions of Cpx are genetically separable, and can be mapped to distinct molecular mechanisms that differentially regulate the SNARE fusion machinery.synapse | neurotransmitter release | exocytosis

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Section: Discussionsupporting

confidence: 77%

Genetic analysis of the Complexin trans-clamping model for cross-linking SNARE complexes in vivo

Cho

Kümmel

et al. 2014

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

102

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“…2B) compared with ϳ0.1 events/s in DKO cells with no syb2. The residual release in this background likely reflects the action of a non-canonical v-SNARE, as has been found to be the case for residual spontaneous release at synapses (25). However, the molecules responsible for residual release in chromaffin cells lacking syb2 and cellubrevin have not been identified.…”

Section: Resultsmentioning

confidence: 96%

Lipid-anchored Synaptobrevin Provides Little or No Support for Exocytosis or Liposome Fusion

Chang¹,

Chiang

Gaffaney

et al. 2016

Journal of Biological Chemistry

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SNARE proteins catalyze many forms of biological membrane fusion, including Ca2؉ -triggered exocytosis. Although fusion mediated by SNAREs generally involves proteins anchored to each fusing membrane by a transmembrane domain (TMD), the role of TMDs remains unclear, and previous studies diverge on whether SNAREs can drive fusion without a TMD. This issue is important because it relates to the question of the structure and composition of the initial fusion pore, as well as the question of whether SNAREs mediate fusion solely by creating close proximity between two membranes versus a more active role in transmitting force to the membrane to deform and reorganize lipid bilayer structure. To test the role of membrane attachment, we generated four variants of the synaptic v-SNARE synaptobrevin-2 (syb2) anchored to the membrane by lipid instead of protein. These constructs were tested for functional efficacy in three different systems as follows: Ca 2؉ -triggered dense core vesicle exocytosis, spontaneous synaptic vesicle exocytosis, and Ca 2؉ -synaptotagmin-enhanced SNARE-mediated liposome fusion. Lipid-anchoring motifs harboring one or two lipid acylation sites completely failed to support fusion in any of these assays. Only the lipid-anchoring motif from cysteine string protein-␣, which harbors many lipid acylation sites, provided support for fusion but at levels well below that achieved with wild type syb2. Thus, lipid-anchored syb2 provides little or no support for exocytosis, and anchoring syb2 to a membrane by a TMD greatly improves its function. The low activity seen with syb2-cysteine string protein-␣ may reflect a slower alternative mode of SNARE-mediated membrane fusion.Nearly all biological fusion mediated by SNARE proteins employs at least one t-SNARE and one v-SNARE anchored to the membrane by a transmembrane domain (TMD) 3 (1-3). Ca 2ϩ -triggered exocytosis of neurotransmitter and hormone from many cells requires the vesicle-SNARE synaptobrevin 2 (syb2) and plasma membrane-SNARE syntaxin, both of which have a TMD (4, 5). Mutations in the TMD alter flux through exocytotic fusion pores in a manner consistent with structural models of fusion pores formed by the TMDs of syntaxin (6, 7) and syb2 (8). Yeast t-and v-SNAREs anchored to membranes by geranylgeranyl moieties instead of a TMD support docking but not fusion (9). SNAREs anchored to membranes by lipid instead of a TMD support lipid mixing of liposomes only when the lipid moiety is long enough to span a lipid bilayer or multiple lipid moieties are present (10) or an accessory protein is present (11).Although early work supported a role of SNARE TMDs in membrane fusion, this issue has become controversial. Recent work on fusion of yeast vacuoles suggests that some SNAREs with lipid anchors can support lipid mixing, content mixing, or both, but other SNAREs cannot function when their TMD is replaced by a lipid anchor (12). Lipid-anchored forms of syntaxin and syb2 were reported to rescue neurotransmitter release at synapses as effectively as wild type ...

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“…Recent evidence suggests that these alternative vesicular SNAREs maintain neurotransmission independently of syb2 (Raingo et al, 2012; Ramirez et al, 2012). Moreover, they also constitute molecular tags for independently functioning SV populations and provide a potential molecular basis for selective regulation of distinct forms of neurotransmitter release (Ramirez and Kavalali, 2012). Earlier work has provided several examples where spontaneous or evoked neurotransmission is differentially sensitive to neuromodulatory signaling cascades (Phillips et al, 2008; Pratt et al, 2011; Ramirez and Kavalali, 2011; Vyleta and Smith, 2011), however, the SV-associated substrates that link this differential regulation to vesicle pool heterogeneity have not yet been identified.…”

Section: Introductionmentioning

confidence: 99%

Reelin Mobilizes a VAMP7-Dependent Synaptic Vesicle Pool and Selectively Augments Spontaneous Neurotransmission

Bal

Leitz

Reese

et al. 2013

Neuron

112

125

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Summary Reelin is a glycoprotein that is critical for proper layering of neocortex during development as well as dynamic regulation of glutamatergic postsynaptic signaling in mature synapses. Here we show that Reelin also acts presynaptically, resulting in robust rapid enhancement of spontaneous neurotransmitter release without affecting properties of evoked neurotransmission. This effect of Reelin requires a modest but significant increase in presynaptic Ca2+ initiated via ApoER2 signaling. The specificity of Reelin action on spontaneous neurotransmitter release is encoded at the level of vesicular SNARE machinery as it requires VAMP7 and SNAP-25 but not synaptobrevin2, VAMP4 or vti1a. These results uncover a novel presynaptic regulatory pathway that utilizes the heterogeneity of synaptic vesicle associated SNAREs and selectively augments action potential-independent neurotransmission.

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The role of non-canonical SNAREs in synaptic vesicle recycling

Cited by 27 publications

References 96 publications

Genetic analysis of the Complexin trans-clamping model for cross-linking SNARE complexes in vivo

Genetic analysis of the Complexin trans-clamping model for cross-linking SNARE complexes in vivo

Lipid-anchored Synaptobrevin Provides Little or No Support for Exocytosis or Liposome Fusion

Reelin Mobilizes a VAMP7-Dependent Synaptic Vesicle Pool and Selectively Augments Spontaneous Neurotransmission

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