title: Functional interaction between amino-acid residues 242 and 290 in cytochromes P-450 2B1 and 2B11.
abstract: Previous studies have revealed the functional importance of the negatively charged amino-acid residue Asp-290 of the phenobarbital-inducible dog liver cytochrome P-450 (P-450) 2B11 (Harlow, G.R. and Halpert J.R. (1996) Arch. Biochem. Biophys. 326, 85-92). A search for P-450 2B11 residues capable of forming a charge pair with Asp-290 suggested the positively charged residue Lys-242 as a likely candidate. Replacement of Lys-242 with Asp in a P-450 2B11 fusion protein with rat NADPH-cytochrome P-450 reductase (reductase) resulted in very low holoenzyme expression levels in Escherichia coli, as did replacement of Asp-290 with Lys. Remarkably, however, expression levels of the double mutant Lys-242 --> Asp/Asp-290 --> Lys were dramatically increased above either single replacement alone. Similarly, the pair-wise substitutions Lys-242 --> Leu/Asp-290 --> Ile in P-450 2B11 and Leu-242 --> Lys/Ile-290 --> Asp in P-450 2B1 showed greater holoenzyme expression levels than the constituent single mutants, providing further evidence for the close proximity of these residues within the three-dimensional structure of these two enzymes. These results support the hypothesis that a functional interaction exists between residues 242 and 290, which may help to coordinate the relative positions of proposed helices G and I. All of the mutant combinations, including the additional P-450 2B11 double mutants Tyr-242/Asn-290 and Tyr-242/Ser-290, displayed altered stereoselectivity of androstenedione hydroxylation.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721, USA. harlow@tonic.pharm.arizona.edu
authors.forename: G R
authors.initials: GR
authors.lastname: Harlow
authors.forename: Y A
authors.initials: YA
authors.lastname: He
authors.forename: J R
authors.initials: JR
authors.lastname: Halpert
mesh_terms: D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000737:chemistry*; D001224:Aspartic Acid / Q000737:chemistry; D002248:Carbon Monoxide; D019362:Cytochrome P-450 CYP2B1 / Q000737:chemistry*; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D000072467:Cytochrome P450 Family 2; D004285:Dogs; D006801:Humans; D008239:Lysine / Q000737:chemistry; D051379:Mice; D016297:Mutagenesis, Site-Directed; D017510:Protein Folding; D011817:Rabbits; D051381:Rats; D011994:Recombinant Proteins; D016415:Sequence Alignment; D013057:Spectrum Analysis; D013250:Steroid Hydroxylases; D013329:Structure-Activity Relationship
chemical_list: D011994:Recombinant Proteins; D001224:Aspartic Acid; D000735:Androstenedione; D002248:Carbon Monoxide; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D019362:Cytochrome P-450 CYP2B1; D000072467:Cytochrome P450 Family 2; C090278:cytochrome P-450 CYP2B11 (dog); D008239:Lysine