Novel CYP2B6 Enzyme Variants in a Rwandese Population: Functional Characterization and Assessment of In Silico Prediction Tools

ABSTRACT Cytochrome P450 CYP2B6 is a highly polymorphic enzyme that metabolizes numerous drugs, pesticides, and environmental toxins. Sequence analysis of a Rwandese population identified eight functionally uncharacterized nonsynonymous variants c.329G>T (p.G110V), c.341T>C (p.I114T), c.444G>T (p.E148D), c.548T>G (p.V183G), c.637T>C (p.F213L), c.758G>A (p.R253H), c.835G>C (p.A279P), and c.1459C>A (p.R487S), and five novel alleles termed CYP2B6*33 to CYP2B6*37 were assigned. Recombinant expression in COS‐1 cells and functional characterization using the antidepressant bupropion and the antiretroviral efavirenz (EFV) as substrates demonstrated complete or almost complete loss‐of‐function for variants p.G110V, p.I114T, p.V183G, and p.F213L, whereas p.E148D, p.R253H, p.A279P, and p.R487S variants were functional. The data were used to assess the predictive power of eight online available functional prediction programs for amino‐acid changes. Although none of the programs correctly predicted the functionality of all variants, substrate docking simulation analyses indicated similar conformational changes by all four deleterious mutations within the enzyme's active site, thus explaining lack of enzymatic function for both substrates. Because low‐activity alleles of CYP2B6 are associated with impaired EFV metabolism and adverse drug response, these results are of potential utility for personalized treatment strategies in HIV/AIDS therapy. This study describes new genetic variants of cytochrome P450 (CYP) 2B6 discovered by a sequencing approach in a prevention of mother‐to‐child HIV transmission cohort from Rwanda and assessment of their functional impact on bupropion and efavirenz hydroxylation activities. Structural modeling and docking analyses helped to understand functional effects of the mutations. Because low‐activity alleles of CYP2B6 are associated with impaired efavirenz metabolism and drug response, these results are of potential utility for personalized treatment strategies in HIV/AIDS therapy.