ZINC-FINGER DOMAINS AND PHORBOL ESTER PHARMACOPHORE - ANALYSIS OF BINDING TO MUTATED FORM OF PROTEIN KINASE-C-TAU AND THE VAV AND C-RAF PROTOONCOGENE PRODUCTS

The phorbol ester binding domain consists of a cysteine-rich region wi th a postulated consensus sequence for binding that includes 15 amino acids (Ahmed, S., Kozma, R., Lee, J., Monfries, C., Harden, N., and Li m, L. (1991) Biochem. J. 280,233-241). In PKC zeta, the only PKC isofo rm lacking phorbol ester binding, this region differs in a single resi due from the consensus (proline in position 11 of the motif). Restorat ion of this proline by site-directed mutagenesis of PKC zeta does not restore binding of either [H-3]phorbol 12,13-dibutyrate or of the ultr apotent ligand [H-3]bryostatin 1, suggesting that even a low affinity ligand interaction is absent. In addition, the vav and c-raf proto-onc ogene products, proteins that possess cysteine-rich regions with high homology to PKC isozymes and other phorbol ester receptors, are unable to bind any of these ligands. Instead, all of these cysteine-rich reg ions bind zinc. Our results suggest that other amino acids besides tho se postulated for the consensus must be necessary for ligand binding a nd argue against direct modulation of PKC zeta, Vav, and c-Raf by phor bol esters.