Clathrin-coated vesicles from human placenta contain GTP-binding proteins.

Biochemical and morphological techniques were used to investigate the GTP-binding proteins of clathrin-coated vesicles. Binding of [3H]GTP to clathrin coats was demonstrated by electron microscopic autoradiography. Purified coated vesicles bound 5.2 pmol [35S]GTP gamma S/mg protein. Addition of GTP or GTP gamma S, but not ATP nor GMP, inhibited binding of [35S]GTP gamma S to intact coated vesicles and Triton X-100-extracted coats. A series of 23-24 kDa GTP-binding proteins with isoelectric points between pH 5-8 were detected in coated vesicles. We suggest that the low molecular weight ras-like GTP-binding protein(s) play a role in regulating vesicle-mediated protein transport or signal transduction within intracellular organelles.