Tyrosine phosphorylation of Munc18-1 inhibits synaptic transmission by preventing SNARE assembly.

Tyrosine kinases are important regulators of synaptic strength. Here, we describe a key component of the synaptic vesicle release machinery, Munc18-1, as a phosphorylation target for neuronal Src family kinases (SFKs). Phosphomimetic Y473D mutation of a SFK phosphorylation site previously identified by brain phospho-proteomics abolished the stimulatory effect of Munc18-1 on SNARE complex formation ("SNARE-templating") and membrane fusion Furthermore, priming but not docking of synaptic vesicles was disrupted in hippocampal -null neurons expressing Munc18-1 Synaptic transmission was temporarily restored by high-frequency stimulation, as well as by a Munc18-1 mutation that results in helix 12 extension, a critical conformational step in vesicle priming.

Regulated exocytosis: merging ideas on fusing membranes.

Cellular trafficking pathways end with fusion reactions at the target. These reactions have been studied extensively for many decades, but recent studies have been particularly productive in providing new solutions to old problems, especially in some of the most complex fusion reactions, like synaptic vesicle secretion in neurons. Here, we discuss new studies that begin to merge ideas on three central questions: (A) are all releasable vesicles equally likely to undergo fusion, (B) do different fusion modes contribute to synaptic transmission, and (C) which molecular events are 'upstream' and which ones 'downstream' of SNARE complex assembly.