An Autoinhibitory Clamp of Actin Assembly Promotes Synaptic Endocytosis

Synaptic membrane-remodeling events such as endocytosis require force-generating actin assembly. The membrane-cytoskeleton remodeling machinery controlling these events localizes to a micron-scale membrane domain called the ‘periactive zone’ (PAZ). However, endocytic events in the PAZ are paradoxically sparse in space and time given the widespread localization of actin and membrane-regulatory PAZ machinery. Here we describe a mechanism whereby autoinhibition clamps the PAZ machinery to limit actin assembly to discrete functional events. We found that collective interactions between the Drosophila PAZ proteins Nwk/FCHSD2, Dap160/Intersectin, and WASp relieve Nwk autoinhibition and promote robust membrane-coupled actin assembly in vitro. Using automated particle tracking to quantify synaptic actin dynamics in vivo, we discovered that Nwk-Dap160 interactions constrain spurious assembly of WASp-dependent actin structures. These interactions also promote synaptic endocytosis, suggesting that autoinhibition both clamps and primes the synaptic endocytic machinery, thereby constraining actin assembly to drive productive membrane remodeling in response to physiological cues.