Regulation of Synaptic Vesicle Budding and Dynamin Function by an EHD ATPase

Eps15 homology domain-containing proteins (EHDs) are conserved ATPases implicated in membrane remodeling. Recently, EHD1 was found to be enriched at synaptic release sites, suggesting a possible involvement in the trafficking of synaptic vesicles. We have investigated the role of an EHD1/3 ortholog (1-EHD) in the lamprey giant reticulospinal synapse. 1-EHD was detected by immunogold at endocytic structures adjacent to release sites. In antibody microinjection experiments, perturbation of 1-EHD inhibited synaptic vesicle endocytosis and caused accumulation of clathrin-coated pits with atypical, elongated necks. The necks were covered with helix-like material containing dynamin. To test whether 1-EHD directly interferes with dynamin function, we used fluid-supported bilayers as in vitro assay. We found that 1-EHD strongly inhibited vesicle budding induced by dynamin in the constant presence of GTP. 1-EHD also inhibited dynamin-induced membrane tubulation in the presence of GTP gamma S, a phenomenon linked with dynamin helix assembly. Our in vivo results demonstrate the involvement of 1-EHD in clathrin/dynamin-dependent synaptic vesicle budding. Based on our in vitro observations, we suggest that 1-EHD acts to limit the formation of long, unproductive dynamin helices, thereby promoting vesicle budding.