Effects of ortho substituent groups of protocatechualdehyde derivatives on binding to the C1 domain of novel protein kinase C.

Diacylglycerol (DAG) regulates a broad range of cellular functions including tumor promotion, apoptosis, differentiation, and growth. Thus, the DAG-responsive C1 domain of protein kinase C (PKC) isoenzymes is considered to be an attractive drug target for the treatment of cancer and other diseases. To develop effective PKC regulators, we conveniently synthesized (hydroxymethyl)phenyl ester analogues targeted to the DAG binding site within the C1 domain. Biophysical studies and molecular docking analysis showed that the hydroxymethyl group, hydrophobic side chains, and acyl group at the ortho position are essential for their interactions with the C1-domain backbone. Modifications of these groups showed diminished binding to the C1 domain. The active (hydroxymethyl)phenyl ester analogues showed more than 5-fold stronger binding affinity for the C1 domain than DAG. Therefore, our findings reveal that (hydroxymethyl)phenyl ester analogues represent an attractive group of C1-domain ligands that can be further structurally modified to improve their binding and activity.