title: Structural insight into the altered substrate specificity of human cytochrome P450 2A6 mutants.
abstract: Human P450 2A6 displays a small active site that is well adapted for the oxidation of small planar substrates. Mutagenesis of CYP2A6 resulted in an increased catalytic efficiency for indole biotransformation to pigments and conferred a capacity to oxidize substituted indoles (Wu, Z.-L., Podust, L.M., Guengerich, F.P. J. Biol. Chem. 49 (2005) 41090-41100.). Here, we describe the structural basis that underlies the altered metabolic profile of three mutant enzymes, P450 2A6 N297Q, L240C/N297Q and N297Q/I300V. The Asn297 substitution abolishes a potential hydrogen bonding interaction with substrates in the active site, and replaces a structural water molecule between the helix B'-C region and helix I while maintaining structural hydrogen bonding interactions. The structures of the P450 2A6 N297Q/L240C and N297Q/I300V mutants provide clues as to how the protein can adapt to fit the larger substituted indoles in the active site, and enable a comparison with other P450 family 2 enzymes for which the residue at the equivalent position was seen to function in isozyme specificity, structural integrity and protein flexibility.
authors.affiliation: Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 N. Torrey Pines Road, MEM-255, La Jolla, CA 92037, USA.
authors.forename: Stefaan
authors.initials: S
authors.lastname: Sansen
authors.forename: Mei-Hui
authors.initials: MH
authors.lastname: Hsu
authors.forename: C David
authors.initials: CD
authors.lastname: Stout
authors.forename: Eric F
authors.initials: EF
authors.lastname: Johnson
mesh_terms: D019943:Amino Acid Substitution; D001189:Aryl Hydrocarbon Hydroxylases / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D001665:Binding Sites; D003198:Computer Simulation; D065637:Cytochrome P-450 CYP2A6; D004789:Enzyme Activation; D006801:Humans; D006899:Mixed Function Oxygenases / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure*; D008956:Models, Chemical; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6