7t81 | pdb_00007t81
Model of Munc13-1 C1-C2B-MUN-C2C 2D crystal between lipid bilayers.
Structural highlights
Function[UN13A_RAT] Plays a role in vesicle maturation during exocytosis as a target of the diacylglycerol second messenger pathway. Involved in neurotransmitter release by acting in synaptic vesicle priming prior to vesicle fusion and participates in the activity-dependent refilling of readily releasable vesicle pool (RRP). Essential for synaptic vesicle maturation in most excitatory/glutamatergic but not inhibitory/GABA-mediated synapses. Also involved in secretory granule priming in insulin secretion.[1] [2] [3] Publication Abstract from PubMedHow can exactly six SNARE complexes be assembled under each synaptic vesicle? Here we report cryo-EM crystal structures of the core domain of Munc13, the key chaperone that initiates SNAREpin assembly. The functional core of Munc13, consisting of C1-C2B-MUN-C2C (Munc13C) spontaneously crystallizes between phosphatidylserine-rich bilayers in two distinct conformations, each in a radically different oligomeric state. In the open conformation (state 1), Munc13C forms upright trimers that link the two bilayers, separating them by approximately 21 nm. In the closed conformation, six copies of Munc13C interact to form a lateral hexamer elevated approximately 14 nm above the bilayer. Open and closed conformations differ only by a rigid body rotation around a flexible hinge, which when performed cooperatively assembles Munc13 into a lateral hexamer (state 2) in which the key SNARE assembly-activating site of Munc13 is autoinhibited by its neighbor. We propose that each Munc13 in the lateral hexamer ultimately assembles a single SNAREpin, explaining how only and exactly six SNARE complexes are templated. We suggest that state 1 and state 2 may represent two successive states in the synaptic vesicle supply chain leading to "primed" ready-release vesicles in which SNAREpins are clamped and ready to release (state 3). Munc13 structural transitions and oligomers that may choreograph successive stages in vesicle priming for neurotransmitter release.,Grushin K, Kalyana Sundaram RV, Sindelar CV, Rothman JE Proc Natl Acad Sci U S A. 2022 Feb 15;119(7). pii: 2121259119. doi:, 10.1073/pnas.2121259119. PMID:35135883[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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