Halogen-π Interactions in the Cytochrome P450 Active Site: Structural Insights into Human CYP2B6 Substrate Selectivity

Numerous cytochrome P450 (CYP) 2B6 substrates including drugs and environmental chemicals are halogenated. To assess the role of halogen-pi bonds in substrate selectivity and orientation in the active site, structures of four CYP2B6 monoterpenoid complexes were solved by Xray crystallography. Bornyl bromide exhibited dual orientations in the active site with the predominant orientation revealing a bromine-pi bond with the Phe108 side chain. Bornane demonstrated two orientations with equal occupancy; in both, the C2 atom that bears the bromine in horny! bromide was displaced by more than 2.5 angstrom compared with the latter complex. The bromine in myrtenyl bromide pi-bonded with Phe297 in CYP2B6, whereas the two major orientations in the active site mutant I114V exhibited bromine-pi interactions with two additional residues, Phe108 and Phe115. Analysis of existing structures suggests that halogen-pi interactions may be unique to the CYP2B enzymes within CYP family 2 but are also important for CYP3A enzymes.