Role of auxilin in uncoating clathrin-coated vesicles

CLATHRIN-coated vesicles transport selected integral membrane proteins from the cell surface and the trans-Golgi network to the endosomal system1,2. Before fusing with their target the vesicles must be stripped of then* coats. This process is effected by the chaperone protein hspTOc together with a 100K cofactor3 which we here identify as the coat protein auxilin. Auxilin binds with high affinity to assembled clathrin lattices and, in the presence of ATP, recruits hsp70c. Dissociation of the lattice does not depend as previously supposed on clathrin light chains or on the amino-terminal domain of the heavy chain4,5. The presence of a J-domain at its carboxy terminus now defines auxilin as a member of the DnaJ protein family. In conjunction with hsp70, DnaJ proteins catalyse protein folding, protein transport across membranes and the selective disruption of protein-protein interactions6–8. We show that deletion of the J-domain of auxilin results in the loss of cofactor activity.