Binding of [26-3H]-epi-bryostatin 4 to protein kinase C

Structure activity analysis of protein kinase C modulators may permit design of selective inhibitors of this important regulatory enzyme. Modeling suggests that the C-26 secondary hydroxyl of bryostatin is homologous to the C-20 primary hydroxyl of phorbol or the C-3 primary hydroxyl of sn-1,2-diacylglycerols (Wender, P. A.; Cribbs, C. M.; Koehler, K. F.; Sharkey, N. A.; Herald, C. L.; Kamano, Y.; Pettit, G. R.; Blumberg, P. M. Modeling of the bryostatins to the phorbol ester pharmacophore on protein kinase C. Proc. Natl. Acad. Sci. USA 85:7197-7201; 1980). We have characterized the binding activity to protein kinase C of the epimer of bryostatin 4 with the configuration at C-26 inverted from R (natural configuration) to S. The Kd of [26-3H]-epi-bryostatin 4 for protein kinase C reconstituted in the presence of phosphatidylserine was 13 +/- 2 nM. [26-3H]-Epi-bryostatin 4 thus retained moderate absolute affinity. Relatively, however, inversion at the chiral center at C-26 caused a dramatic decrease in binding affinity. Binding of [26-3H]-epi-bryostatin 4 was competitively inhibited by phorbol 12,13-diacetate, as expected for ligands that interact at the same binding site.