Presence of cyclic nucleotide-Ca2+ independent protein kinase in bovine brain coated vesicles

Abstract

Coated vesicles, which are membrane vesicles enclosed by a polyhedral protein lattice, are involved in many cellular events, including intracellular membrane transport and protein secretion, in which they must be able to undergo repeated membrane fusion and fission. The icosahedral lattice of protein surrounding the core of coated vesicles is composed predominantly of clathrin, a 180,000 (180 K) molecular weight protein, and other 30K and 36K polypeptides. In native conditions, the basic subunit of the coat consists of a trimer of clathrin with probably three polypeptides of 30K and/or 36K (refs 9-11). Additional minor proteins of 100K and 55K have been reported in purified coated vesicles. We describe here the presence of cyclic nucleotide- and Ca2+-independent protein kinase activity in coated vesicles. This protein kinase phosphorylates specifically a unique 50K protein which can be co-purified with clathrin and seems to be an integral protein of coated vesicles.