Binding to Rab3A-interacting molecule RIM regulates the presynaptic recruitment of Munc13-1 and ubMunc13-2

Abstract

Transmitter release at synapses between nerve cells is spatially restricted to active zones, where synaptic vesicle docking, priming, and Ca 2+-dependent fusion take place in a temporally highly coordinated manner. Munc13s are essential for priming synaptic vesicles to a fusion competent state, and their specific active zone localization contributes to the active zone restriction of transmitter release and the speed of excitation-secretion coupling. However, the molecular mechanism of the active zone recruitment of Munc13s is not known. We show here that the active zone recruitment of Munc13 isoforms Munc13-1 and ubMunc13-2 is regulated by their binding to the Rab3A-interacting molecule RIM1α, a key determinant of long term potentiation of synaptic transmission at mossy fiber synapses in the hippocampus.Weidentify a single point mutation in Munc13-1 and ubMunc13-2 (I121N) that, depending on the type of assay used, strongly perturbs or abolishes RIM1α binding in vitro and in cultured fibroblasts, and we demonstrate that RIM1α binding-deficient ubMunc13-2I121 is not efficiently recruited to synapses. Moreover, the levels of Munc13-1 and ubMunc13-2 levels are decreased in RIM1α-deficient brain, and Munc13-1 is not properly enriched at active zones of mossy fiber terminals of the mouse hippocampus if RIM1α is absent. We conclude that one function of the Munc13/RIM1α interaction is the active zone recruitment of Munc13-1 and ubMunc13-2. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.