Functional analysis of interaction sites on the N-terminal domain of clathrin heavy chain.

In clathrin-mediated membrane traffic, clathrin does not bind directly to cargo and instead binds to adaptors that mediate this function. For endocytosis, the main adaptor is the adaptor protein (AP)-2 complex, but it is uncertain how clathrin contacts AP-2. Here we tested in human cells the importance of the three binding sites that have been identified so far on the N-terminal domain (NTD) of clathrin. We find that mutation of each of the three sites on the NTD, alone or in combination, does not block clathrin/AP-2-mediated endocytosis in the same way as deletion of the NTD. We report here the fourth and final site on the NTD that is required for clathrin/AP-2-mediated endocytic function. Each of the four interaction sites can operate alone to mediate endocytosis. The observed functional redundancy between interaction sites on the NTD explains how productivity of clathrin-coated vesicle formation is ensured.