Synaptic distribution of the endocytic accessory proteins AP180 and CALM.

Clathrin-coated vesicles mediate a variety of endocytosis pathways in cells, including endocytic events at synapses. AP180 and clathrin assembly lymphoid myeloid leukemia protein (CALM) are clathrin accessory proteins that promote the formation of clathrin-coated vesicles. Both proteins bind to membrane lipids through their epsin N-terminal homology domains and interact with clathrin and related protein components through their carboxyl-terminal peptide motifs. We examine their neuronal expression and synaptic distribution. We show that both proteins are detected in synapses but demonstrate different distribution patterns. AP180 is located predominantly in presynaptic profiles, whereas CALM is found nonselectively in pre- and postsynaptic profiles and also in perisynaptic processes. These observations reveal an unexpected relationship between AP180 and the presumed non-neuronal homologue CALM. We propose that both AP180 and CALM function as endocytic accessory proteins at synapses, but each may regulate distinct clathrin pathways.