Functional influence of human CYP2D6 allelic variations: P34S, E418K, S486T, and R296C.

CYP2D6 is responsible for the oxidative metabolism of 20-25 % of clinical drugs and its genetic polymorphisms can significantly influence the drug metabolism. In this study, we analyzed the functional activities of four nonsynonymous single nucleotide polymorphisms from CYP2D6*52 allele, which were recently found, and one found frequently in CYP2D6 alleles. Recombinant variant enzymes of E418K, S486T, and R296C were successfully expressed in Escherichia coli and purified. However, a CYP holoenzyme spectrum of P34S variant was not detected in E. coli whole cell level. Structural analysis indicated that P34S mutation seemed to perturb a highly conserved proline-rich N-terminus of CYP2D6. Steady state kinetic analyses showed the significant reductions of enzymatic activities in E418K and R296C variants. In the case of bufuralol 1'-hydroxylation, a novel mutant, E418K, showed 32 % decrease in catalytic efficiency (k cat/K m) mainly due to the decrease of k cat value. R296C showed much greater reduction in the catalytic efficiency (9 % of wild-type) due to both of a decrease of k cat value and an increase of K m value. In the case of dextromethorphan O-demethylation, E418K showed both of a decrease of k cat value and an increase K m value to result in ~43 % reduction of catalytic efficiency. A highly decreased catalytic efficiency (~6 % of wild-type) in the mutant of R296C also was observed mainly due to the dramatic change of k cat value of dextromethorphan O-demethylation. These results suggested that individuals carrying these allelic variants are likely to have the altered metabolic abilities of many clinical drugs therefore, these polymorphisms of CYP2D6 should be much concerned for reliable drug treatment.