RIM proteins activate vesicle priming by reversing autoinhibitory homodimerization of Munc13.
At a synapse, the presynaptic active zone mediates synaptic vesicle exocytosis. RIM proteins are active zone scaffolding molecules that--among others--mediate vesicle priming and directly or indirectly interact with most other essential presynaptic proteins. In particular, the Zn²+ finger domain of RIMs binds to the C₂A domain of the priming factor Munc13, which forms a homodimer in the absence of RIM but a heterodimer with it. Here, we show that RIMs mediate vesicle priming not by coupling Munc13 to other active zone proteins as thought but by directly activating Munc13. Specifically, we found that the isolated Zn²+ finger domain of RIMs autonomously promoted vesicle priming by binding to Munc13, thereby relieving Munc13 homodimerization. Strikingly, constitutively monomeric mutants of Munc13 rescued priming in RIM-deficient synapses, whereas wild-type Munc13 did not. Both mutant and wild-type Munc13, however, rescued priming in Munc13-deficient synapses. Thus, homodimerization of Munc13 inhibits its priming function, and RIMs activate priming by disrupting Munc13 homodimerization.
Department of Molecular and Cellular Physiology, Stanford University, Lorry Lokey Building, 265 Campus Drive, Stanford, CA 94305-5453, USA.
Lunbin
L
Deng
Pascal S
PS
Kaeser
Wei
W
Xu
Thomas C
TC
Südhof
D000818:Animals; D019281:Dimerization; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013572:Synaptic Vesicles / Q000378:metabolism*; D016335:Zinc Fingers; D020692:rab3 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D009419:Nerve Tissue Proteins; C491490:Rims1 protein, mouse; C503321:Unc13a protein, mouse; D019204:GTP-Binding Proteins; C475524:Rim2 protein, mouse; D020692:rab3 GTP-Binding Proteins
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