title: Identification and functional characterization of a new CYP2C9 variant (CYP2C9*5) expressed among African Americans.
abstract: CYP2C9 is a polymorphic gene for which there are four known allelic variants; CYP2C9*1, CYP2C9*2, CYP2C9*3, and CYP2C9*4. In the present study, DNA from 140 European Americans and 120 African Americans was examined by single-strand conformational polymorphism and restriction fragment length polymorphism analyses, resulting in the identification of a new CYP2C9 variant, CYP2C9*5. This variant is derived from a C1080G transversion in exon 7 of CYP2C9 that leads to an Asp360Glu substitution in the encoded protein. The CYP2C9*5 variant was found to be expressed only in African Americans, such that approximately 3% of this population carries the CYP2C9*5 allele. The variant was expressed in, and purified from, insect cells infected with a recombinant baculovirus. Comparative kinetic studies using the purified wild-type protein CYP2C9*1; the Ile359Leu variant, CYP2C9*3; and the Asp360Glu variant, CYP2C9*5 were carried out using (S)-warfarin, diclofenac, and lauric acid as substrates. The major effect of the Asp360Glu mutation was to increase the K(m) value relative to that of CYP2C9*1 for all three substrates: 12-fold higher for (S)-warfarin 7-hydroxylation, 5-fold higher for the 4'-hydroxylation of diclofenac, and 3-fold higher for the omega-1 hydroxylation of lauric acid. V(max) values differed less than K(m) values between the CYP2C9*1 and CYP2C9*5 proteins. In vitro intrinsic clearances for CYP2C9*5, calculated as the ratio of V(max)/K(m), ranged from 8 to 18% of CYP2C9*1 values. The corresponding ratio for CYP2C9*3 was 4 to 13%. Accordingly, the in vitro data suggest that carriers of the CYP2C9*5 allele would eliminate CYP2C9 substrates at slower rates relative to persons expressing the wild-type protein.
authors.affiliation: Department of Medicinal Chemistry, University of Washington, Seattle, Washington, USA.
authors.forename: L J
authors.initials: LJ
authors.lastname: Dickmann
authors.forename: A E
authors.initials: AE
authors.lastname: Rettie
authors.forename: M B
authors.initials: MB
authors.lastname: Kneller
authors.forename: R B
authors.initials: RB
authors.lastname: Kim
authors.forename: A J
authors.initials: AJ
authors.lastname: Wood
authors.forename: C M
authors.initials: CM
authors.lastname: Stein
authors.forename: G R
authors.initials: GR
authors.lastname: Wilkinson
authors.forename: U I
authors.initials: UI
authors.lastname: Schwarz
mesh_terms: D001741:Black or African American; D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases; D044383:Black People / Q000235:genetics*; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D006801:Humans; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase