Analysis of 100-180-kDa phosphoproteins in clathrin-coated vesicles from bovine brain

Abstract

Protein kinases which co-purify with clathrin-coated vesicles are known to phosphorylate in vitro the 50-kDa subunit of the HA-II adaptor complex and upon inclusion of polylysine the beta-light chain of clathrin and polypeptides above 100 kDa. Here we relate the high molecular mass phosphoproteins to the known subunits of the adaptor protein complexes and to other clathrin-associated proteins by means of immunoprecipitation with monoclonal antibodies, two-dimensional electrophoresis, or electrophoresis in urea-sodium dodecyl sulfate-polyacrylamide gels. Our results show that some of the labeling of the 100-120-kDa region is accounted for by the beta'- and gamma-subunits of the HA-I adaptor complex, the alpha a-, and, to a lesser extent, by the beta-subunits of the HA-II adaptor complex. In addition, we found the assembly protein AP 180 and a hitherto undescribed 110-kDa coat polypeptide to be heavily phosphorylated upon release of these proteins from the coated vesicle membrane. In all cases, labeling was confined to serine residues.