Primary Substrate Specificity Determinants for the H4‐Specific Protease‐Activated Protein Phosphotransferase

Abstract

The specificity of the histone‐H4‐specific, protease‐activated protein kinase (H4‐PK) was examined using two series of synthetic peptides corresponding to the phosphorylation sites in histone H4 and pyruvate kinase. Optimum kinetic constants for phosphorylation were observed using the peptide Val‐Lys‐Arg‐Ile‐Ser‐Gly‐Leu. Peptides in which the Lys was replaced by Arg or the Lys‐Arg sequence was transposed were phosphorylated with less favorable kinetics. Peptides with either basic residue deleted did not serve as substrates. Only the H4 peptide, containing an Arg‐Arg sequence, was phosphorylated by the cyclic‐AMP‐dependent protein kinase (CA‐PK). Distinct specificity determinants for H4‐PK and CA‐PK were also observed using the pyruvate kinase peptide (Leu‐Arg‐Arg‐Ala‐Ser‐Leu‐Gly). Collectively the data indicated that the primary substrate specificity determinants for H4‐PK are Lys‐Arg‐Xaa‐Ser whereas the CA‐PK selectively phosphorylates the sequence Arg‐Arg‐Xaa‐Ser.