Phosphorylation and activation of cGMP-dependent protein kinase by Src

Abstract

Using information obtained from experiments with peptide substrates of v-Src, a motif within the cGMP-binding domain of cGMP-dependent protein kinase (cGK) was identified as a potential phosphorylation site for v-Src. Here we show that the purified Iα isozyme of cGK is phosphorylated stoichiometrically and in a time-dependent manner by purified Src in vitro. The kinase activity of cGK is elevated approximately 4-fold (relative to autophosphorylated cGK) or 10-fold (relative to unphosphorylated cGK) upon tyrosine phosphorylation by Src. Phosphorylation of cGK by v-Src produces modest effects on the cGMP-binding properties and dissociation rates of cGK, and reduces the k act for cGMP. We hypothesize that the mechanism of activation may involve coupling of the cGMP binding domain to the catalytic domain.