title: Active site topology of Saccharomyces cerevisiae lanosterol 14 alpha-demethylase (CYP51) and its G310D mutant (cytochrome P-450SG1).
abstract: Incubation of phenyldiazene (PhN = NH) with lanosterol 14 alpha-demethylase, a cytochrome P-450 enzyme (CYP51) that oxidatively removes the 14 alpha-methyl group of lanosterol, results in the appearance of a 478-nm band indicative of phenyl-iron complex formation. In situ oxidation of the phenyl-iron complex by ferricyanide yields exclusively the N-phenylprotoporphyrin IX regioisomer with the phenyl group on the nitrogen of pyrrole ring C (NC). The biphenyl-iron complex formed in the analogous reaction of the enzyme with biphenyldiazene similarly rearranges on treatment with ferricyanide to the NC regioisomer of N-biphenylprotoporphyrin IX. The active site cavity must therefore be at least 10 A high directly above the iron atom and pyrrole ring C of the heme group, and lanosterol binds to the enzyme in the region above pyrrole ring C. Phenyl-iron complex formation is not detected spectroscopically with cytochrome P-450SG1, a catalytically inactive G310D mutant of lanosterol 14 alpha-demethylase in which the sixth iron coordination site is thought to be occupied by an imidazole ligand. Nevertheless, oxidation of the phenyldiazene-treated enzyme with ferricyanide provides the NA and NC regioisomers of N-phenylprotoporphyrin IX in a 40:60 ratio. The single amino acid substitution in cytochrome P-450SG1 thus causes a conformational change that retracts the amino acid residues that cover pyrrole ring A and moves an imidazole ligand into the active site.
authors.affiliation: Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco 94143-0446.
authors.forename: S F
authors.initials: SF
authors.lastname: Tuck
authors.forename: Y
authors.initials: Y
authors.lastname: Aoyama
authors.forename: Y
authors.initials: Y
authors.lastname: Yoshida
authors.forename: P R
authors.initials: PR
authors.lastname: Ortiz de Montellano
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000235:genetics; D005292:Ferricyanides / Q000737:chemistry; D007097:Imines / Q000737:chemistry; D009154:Mutation; D009211:Myoglobin / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D058886:Sterol 14-Demethylase
chemical_list: D005292:Ferricyanides; D007097:Imines; D009211:Myoglobin; D003577:Cytochrome P-450 Enzyme System; C011981:phenyldiazene; D010088:Oxidoreductases; D058886:Sterol 14-Demethylase