Functional malleability of the carboxyl-terminal tail in protein kinase A

The catalytic (C) subunit of protein kinase A (PKA) is regarded as a framework for the protein kinase family. Its sequence is composed of a conserved core (residues 40-300) between two segments at the amino and carboxyl termini of the protein. Since the various protein kinases differ in their specificity, it seems reasonable to assume that these nonhomologous segments may be involved in endowing each kinase with its individual specificity. Here we present data to show that the cluster of acidic amino acids ((328)DDYEEEE(334)) at the carboxyl-terminal ''tail'' of the C subunit, specifically Tyr(330), contributes to its substrate recognition. This is based on three complementary lines of evidence: (i) on a conformation-sensitive cleavage of the C subunit by a kinase-splitting membranal proteinase that specifically recognizes this cluster, to demonstrate the occurrence in solution of ''open'' (cleavable) and ''closed'' (noncleavable) conformations of the C subunit; (ii) on analysis of the three-dimensional structures of the open and closed conformations of the C subunit, showing an similar to 7-Angstrom movement of the phenolic hydroxyl of Tyr(330) to reach (in the closed conformation) an similar to 3-Angstrom distance from the nitrogen atoms of the Arg residue at position p-3 of the PKA consensus sequence; and (iii) on single-site mutations of the C subunit (e.g. Y330A) that show a significant contribution of Tyr(330) to the K-m of PKA for its substrates/inhibitors and to its catalytic efficacy (V-max/K-m).