PRECISION TARGETING OF PROTEIN-KINASES - AN AFFINITY LABEL THAT INACTIVATES THE CGMP-DEPENDENT BUT NOT THE CAMP-DEPENDENT PROTEIN-KINASE

Although the cAMP-dependent (PKA) and cGMP-dependent protein kinases ( PKG) usually participate in unrelated biological processes, their enzy mological properties are decidedly similar, Based upon the multitude o f comparative studies conducted to date, it appears that these two enz ymes exhibit very similar peptide substrate specificities, Furthermore , most inhibitors that have been reported for PKG serve in a nearly eq ual capacity for PKA, Consequently, the task of distinguishing between these enzymes, especially under in vivo conditions, has proved to be daunting, However, we have recently found that PKA will only phosphory late non-amino acid residues whose alpha-configuration corresponds to that found in L-amino acids, whereas PKG will catalyze the phosphoryla tion of residues corresponding to both L- and D-amino acids (Wood, J., Mendelow, M., Yan, X., Corbin, J. D., Francis, S. H., and Lawrence, D . S. (1996) J. Biol. Chem. 271, 174-179). Based upon these results, we have designed a potent affinity label for PKG (K-I = 21.1 +/- 4.7 mu M), that has no measurable activity toward PKA, This represents the fi rst example of an peptide-based inactivator that fully distinguishes b etween these two closely related enzymes, These results suggest that a similar strategy may provide highly specific inactivators for other p rotein kinases as well.