Protein kinase C pseudosubstrate prototope: structure-function relationships.

A structure-function study of the protein kinase C (PK-C) pseudosubstrate sequence (R19FARK-GALRQKNV31) has been undertaken. The role of specific residues was investigated using an alanine substitution scan. Arg-22 was the most important determinant in the inhibitor sequence, since substitution of this residue by alanine gave a 600-fold increase in the IC50 value to 81 +/- 9 microM. Substitutions of other basic residue also increased the IC50, 5-, 11- and 24-fold for the Ala-19, Ala-23 and Ala-27 substitutions, respectively. The importance of basic residues in determining the potency of the pseudosubstrate peptide reflects the requirements for these residues in peptide substrate phosphorylation. The residues Gly-24, Leu-26 and Gln-28 were also important for pseudosubstrate inhibitor potency. The large difference in the IC50 value for the [A22]PK-C(19-31) peptide makes it a valuable control in studies employing the pseudosubstrate peptide to explore functional roles of PK-C.