Abstract
Phosphatidylinositol-4,5-bisphosphate [PI(4,5)P&sub2;] plays a fundamental role in clathrin-mediated endocytosis. However, precisely how PI(4,5)P&sub2; metabolism is spatially and temporally regulated during membrane internalization and the functional consequences of endocytosis-coupled PI(4,5)P&sub2; dephosphorylation remain to be explored. Using cell-free assays with liposomes of varying diameters, we show that the major synaptic phosphoinositide phosphatase, synaptojanin 1 (Synj1), acts with membrane curvature generators/sensors, such as the BAR protein endophilin, to preferentially remove PI(4,5)P&sub2; from curved membranes as opposed to relatively flat ones. Moreover, in vivo recruitment of Synj1's inositol 5-phosphatase domain to endophilin-induced membrane tubules results in fragmentation and condensation of these structures largely in a dynamin-dependent fashion. Our study raises the possibility that geometry-based mechanisms may contribute to spatially restricting PI(4,5)P&sub2; elimination during membrane internalization and suggests that the PI(4,5)P&sub2;-to-PI4P conversion achieved by Synj1 at sites of high curvature may cooperate with dynamin to achieve membrane fission.