The specificity of the protein kinase C alpha, betaII and gamma isoforms as assessed by an unnatural alcohol-appended peptide library.

Previous studies using conventional peptide-based libraries have demonstrated that homologous protein-processing enzymes [e.g. the alpha, betaII and gamma isoforms of protein kinase (PKC)] typically display identical amino acid consensus sequences. These observations have hampered the acquisition of selective synthetic substrates for the individual members of these enzyme families. We describe here a parallel synthesis strategy, readily adaptable to the preparation of large libraries, that has led to the emergence of the first examples of selective substrates for the conventional PKC isoforms. In addition, we have found that a wide variety of structurally diverse N-appended alcohol-containing residues, including tyrosine, serve as substrates for the PKC alpha, betaII and gamma isoforms. This broad active-site substrate specificity with respect to both natural and unnatural residues may prove to be especially applicable to the construction of transition-state analogues and suicide substrates, species that often require the presence of structurally elaborate functionality.