A SITE OF INTERACTION BETWEEN PLECKSTRINS PH DOMAINS AND G(BETA-GAMMA)

Pleckstrin is a 40 kDa substrate for protein kinase C found in platele ts and neutrophils. Based upon its sequence, pleckstrin contains two o f the recently-described PH domains that are thought to be binding mot ifs for phosphatidyl 4,5-bisphosphate (PIP2) and/or G protein beta gam ma heterodimers (G(beta gamma)). In the present studies we have examin ed the interaction between pleckstrin and G(beta gamma) by incubating pleckstrin fusion proteins with lysates from human platelets. In this analysis, both the N-terminal and C-terminal PH domains from pleckstri n bound G(beta gamma) in vitro, as did peptides containing as little a s the first 30 residues of the C-terminal pleckstrin PH domain. Introd uction of a point mutation into this region, analogous to the mutation in the Btk PH domain that causes X-linked immunodeficiency disease (X ID) in mice, dramatically disrupted this interaction. We propose that pleckstrin may interact with G(beta gamma) and that one potential site for this interaction involves the first 30 residues of pleckstrin's C -terminal PH domain.