Received for publication May 5, 2008.
Revised June 30, 2008.
Accepted for publication June 30, 2008.

Re-Engineering of CYP2C9 to Probe Acid-Base Substrate Selectivity

Abstract

A common feature of many CYP2C9 ligands is their weak acidity. As revealed by crystallography, the structural basis for this behavior involves a charge-pairing interaction between an anionic moiety on the substrate and an active site R108 residue. In the present study we attempted to re-engineer CYP2C9 to better accept basic ligands by charge-reversal at this key residue. We expressed and purified the R108E and R108E/D293N mutants and compared their ability with that of native CYP2C9 to interact with (S)-warfarin, diclofenac, pyrene, propranolol and ibuprofen amine. As expected, the R108E mutant maintained all of the native enzyme's pyrene 1-hydroxylation activity, but catalytic activity towards diclofenac and (S)-warfarin was abrogated. In contrast, the double mutant displayed much less selectivity in its behavior towards these control ligands. Neither mutants displayed significant enhancement of propranolol metabolism and all three preparations exhibited a Type II (inhibitor) rather than Type I (substrate) spectrum with ibuprofen amine, although binding became progressively weaker with the single and double mutants. Collectively, these data underscore the importance of the amino acid at position 108 in the acid substrate selectivity of CYP2C9, highlight the accommodating nature of the CYP2C9 active site, and provide a cautionary note regarding facile re-engineering of these complex P450 active sites.

Key words: CYP2C, cytochrome P450 function, cytochrome P450 structure