GAP-43 AUGMENTATION OF G-PROTEIN-MEDIATED SIGNAL-TRANSDUCTION IS REGULATED BY BOTH PHOSPHORYLATION AND PALMITOYLATION

The neuronal protein GAP-43 is concentrated at the growth cone membran e, where it is thought to amplify the signal transduction process. As a model for its neuronal effects, GAP-43 protein injection into Xenopu s laevis oocytes strongly augments the calcium-sensitive chloride curr ent evoked by the G protein-coupled receptor stimulation. We have now examined a series of GAP-43 mutants in this system and determined thos e regions of GAP-43 required far this increase in current flux. As exp ected, palmitoylation inhibits signal amplification in oocytes by bloc king G protein activation. Unexpectedly, a second domain of GAP-43 (re sidues 35-50) containing a protein kinase C phosphorylation site at re sidue 41 is also necessary for augmentation of G protein-coupled signa ls in oocytes. This region is not required for activation of isolated G(o) but is necessary for GAP-43 binding to isolated calmodulin and to isolated protein kinase C. Substitution of Asp for Ser(41) inactivate s GAP-43 as a signal facilitator in oocytes. This mutation blocks GAP- 43 binding to both protein kinase C and calmodulin. Thus, GAP-43 regul ates an oocyte signaling cascade via coordinated, simultaneous G prote in activation and interaction with either calmodulin or protein kinase C.