Ca2+-dependent release of synaptotagmin-1 from the SNARE complex on phosphatidylinositol 4,5-bisphosphate-containing membranes

Voleti, Rashmi; Jaczynska, Klaudia; Rizo, Josep

doi:10.7554/elife.57154

Cited by 59 publications

(174 citation statements)

References 72 publications

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“…3B. As observed in recent experiments and our previous simulations, Ca 2+ binding triggered Syt-SNARE bond dissociation, because it is highly energetically favorable for Ca 2+ -bound C2B domains to insert their Ca 2+ -binding loops into the PM, a configuration that is sterically incompatible with binding to a fully zippered SNARE complex (35,57).…”

Section: Simulations Of the Full Machinery: Ca 2+ -Mediated Unclamping And Fusionsupporting

confidence: 77%

SNAREs and Synaptotagmin cooperatively determine the Ca²⁺ sensitivity of neurotransmitter release in fixed stoichiometry modules

2021

Preprint

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Neurotransmitter release is accomplished by a multi-component machinery including the membrane-fusing SNARE proteins and Ca2+-sensing Synaptotagmin molecules. However, the Ca2+ sensitivity of release was found to increase or decrease with more or fewer SNARE complexes at the release site, respectively, while the cooperativity is unaffected (Acuna et al., 2014; Arancillo et al., 2013), suggesting that there is no simple division of labor between these two components. To examine the mechanisms underlying these findings, we developed molecular dynamics simulations of the neurotransmitter release machinery, with variable numbers of Synaptotagmin molecules and assembled SNARE complexes at the release site. Ca2+ uncaging simulations showed that increasing the number of SNARE complexes at fixed stoichiometric ratio of Synaptotagmin to SNAREs increased the Ca2+ sensitivity without affecting the cooperativity. The physiological cooperativity of ~4-5 was reproduced with 2-3 Synaptotagmin molecules per SNARE complex, suggesting that Synaptotagmin and SNAREs cooperate in fixed stoichiometry modules. In simulations of action potential-evoked release, increased numbers of Synaptotagmin-SNARE modules increased release probability, consistent with experiment. Our simulations suggest that the final membrane fusion step is driven by SNARE complex-mediated entropic forces, and by vesicle-tethering forces mediated by the long Synaptotagmin linker domains. In consequence, release rates are increased when more SNARE complexes and Synaptotagmin monomers are present at the fusion site.

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Section: Simulations Of the Full Machinery: Ca 2+ -Mediated Unclamping And Fusionsupporting

confidence: 77%

SNAREs and Synaptotagmin cooperatively determine the Ca²⁺ sensitivity of neurotransmitter release in fixed stoichiometry modules

2021

Preprint

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“…2. Consistent with the Syt-SNARE primary interaction contributing to clamping, spontaneous release frequencies are increased when the binding interface is disrupted but unaltered by mutations that strengthen it (Voleti et al, 2020;Zhou et al, 2015). In simulations, Ca 2+ entry triggered ring disassembly and release of SNAREs by Ca 2+ -dependent membrane insertion of the C2B Ca 2+ -binding loops that sequestered the C2B domains, Fig.…”

Section: Syt Clamps Release By Spacing Membranes and Sequestering Snare Complexesmentioning

confidence: 54%

“…4, and the shedding of Syt C2B-bound SNAREpins following membrane insertion of C2B Ca 2+ -binding loops. The shedding is due to structural constraints imposed by the SNARE-C2B complex (Voleti et al, 2020), Fig. 3.…”

Section: Discussionmentioning

confidence: 99%

Coupling of Ca²⁺-triggered unclamping and membrane fusion during neurotransmitter release

Polley

Zeng

et al. 2021

Preprint

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Neurotransmitter (NT) release is accomplished by a machinery that unclamps fusion in response to calcium and then fuses the synaptic vesicle and plasma membranes. These are often thought of as distinct tasks assigned to non-overlapping components. Vesicle release rates have a power law dependence on [Ca2+] with an exponent of 3-5, long taken to indicate that 3-5 Ca2+ ions bind the calcium sensor Synaptotagmin to trigger release. However, dependencies at low [Ca2+] are inconsistent with simple sequential binding to a single Ca2+ sensor followed by a final fusion step. Here we developed coarse-grained molecular dynamics simulations of the NT release machinery accounting for Synaptotagmin-mediated unclamping and SNARE-mediated fusion. Calcium-triggered unclamping and SNARE-mediated fusion emerged from simulations as contemporaneous, coupled processes. Increasing cytosolic [Ca2+], the instantaneous fusion rate increased as SNAREpins were progressively and reversibly released by dissociation of Synaptotagmin-SNAREpin complexes. Simulations reproduced the observed dependence of release rates on [Ca2+], but the power law was unrelated to the number of Ca2+ ions required. Action potential-evoked vesicle release probabilities depended on the number of transiently unclamped SNAREpins, explaining experimental dependencies of release probabilities on both unclamping and membrane-fusing machinery components. These results describe a highly cooperative NT release machinery with intrinsically inseparable unclamping and membrane-fusing functionalities.

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“…Deletion of Syt greatly increased spontaneous release in mice (14,15) and Drosophila (16)(17)(18). The mechanism is unknown, but it was proposed that Syt may clamp fusion in the absence of Ca 2+ by imposing a membrane separation too great for SNAREmediated fusion (19), or by binding SNAREs and locking them in a fusion-incompetent state (20)(21)(22). Whatever the mechanism, a critical role is likely played by Syt-SNARE binding, recently characterized by structural studies (23)(24)(25).…”

Section: Introductionmentioning

confidence: 99%

Synaptotagmin rings as high sensitivity regulators of synaptic vesicle docking and fusion

Zhu¹,

McDargh

Li³

et al. 2021

Preprint

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Synchronous release at neuronal synapses is accomplished by a machinery that senses calcium influx and fuses the synaptic vesicle and plasma membranes to release neurotransmitters. Previous studies suggested the calcium sensor Synaptotagmin (Syt) is a facilitator of vesicle docking and both a facilitator and inhibitor of fusion. On phospholipid monolayers, the Syt C2AB domain spontaneously oligomerized into rings that are disassembled by Ca2+, suggesting Syt rings may clamp fusion as membrane-separating "washers" until Ca2+-mediated disassembly triggers fusion and release (Wang et al., 2014). Here we combined mathematical modeling with experiment to measure mechanical properties of Syt rings and to test this mechanism. Consistent with experiment, the model quantitatively recapitulates observed Syt ring-induced dome and volcano shapes on phospholipid monolayers, and predicts rings are stabilized by anionic phospholipid bilayers or bulk solution with ATP. The selected ring conformation is highly sensitive to membrane composition and bulk ATP levels, a property that may regulate vesicle docking and fusion in ATP-rich synaptic terminals. We find the Syt molecules hosted by a synaptic vesicle oligomerize into a halo, unbound from the vesicle, but in proximity to sufficiently PIP2-rich plasma membrane (PM) domains the PM-bound trans Syt ring conformation is preferred. Thus, the Syt halo serves as landing gear for spatially directed docking at PIP2-rich sites that define the active zones of exocytotic release, positioning the Syt ring to clamp fusion and await calcium. Our results suggest the Syt ring is both a Ca2+-sensitive fusion clamp and a high-fidelity sensor for directed docking.

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Ca2+-dependent release of synaptotagmin-1 from the SNARE complex on phosphatidylinositol 4,5-bisphosphate-containing membranes

Cited by 59 publications

References 72 publications

SNAREs and Synaptotagmin cooperatively determine the Ca²⁺ sensitivity of neurotransmitter release in fixed stoichiometry modules

SNAREs and Synaptotagmin cooperatively determine the Ca²⁺ sensitivity of neurotransmitter release in fixed stoichiometry modules

Coupling of Ca²⁺-triggered unclamping and membrane fusion during neurotransmitter release

Synaptotagmin rings as high sensitivity regulators of synaptic vesicle docking and fusion

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Ca2+-dependent release of synaptotagmin-1 from the SNARE complex on phosphatidylinositol 4,5-bisphosphate-containing membranes

Cited by 59 publications

References 72 publications

SNAREs and Synaptotagmin cooperatively determine the Ca2+ sensitivity of neurotransmitter release in fixed stoichiometry modules

SNAREs and Synaptotagmin cooperatively determine the Ca2+ sensitivity of neurotransmitter release in fixed stoichiometry modules

Coupling of Ca2+-triggered unclamping and membrane fusion during neurotransmitter release

Synaptotagmin rings as high sensitivity regulators of synaptic vesicle docking and fusion

Contact Info

Product

Resources

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SNAREs and Synaptotagmin cooperatively determine the Ca²⁺ sensitivity of neurotransmitter release in fixed stoichiometry modules

SNAREs and Synaptotagmin cooperatively determine the Ca²⁺ sensitivity of neurotransmitter release in fixed stoichiometry modules

Coupling of Ca²⁺-triggered unclamping and membrane fusion during neurotransmitter release