Modulation of protein-ligand interactions by photocleavage of a cyclic peptide using phosphatidylinositol 3-kinase SH3 domain as model system.

To photomodulate the interaction of the phosphatidylinositol 3-kinase SH3 domain with a peptide ligand, a cyclic peptide (cyclic-1) with a photolabile side chain-to-side chain linker was synthesized. The conformation of cyclic-1 differs from that of the parent linear peptide, but becomes identical by UV-irradiation. Accordingly, the binding affinity of cyclic-1 to the SH3 domain increased upon conversion of the cyclic to a linear flexible structure by irradiation (K(d): 3.4 +/- 1.7 and 0.9 +/- 0.3 mM, respectively). These results confirm the usefulness of a photocleavable peptide for photocontrol of peptide-protein interactions.