A new CYP3A5 variant, CYP3A5*11, is shown to be defective in nifedipine metabolism in a recombinant cDNA expression system.

A new CYP3A5 variant, CYP3A511, was found in a white European subject by DNA sequencing. The CYP3A511 allele contains a single nucleotide polymorphism (SNP) (g.3775A>G) in exon 2, which results in a Tyr53Cys substitution, and a g.6986A>G splice change, the latter SNP previously reported in the defective CYP3A53 allele. However, the CYP3A53 is not a null allele because this variant is associated with leaky splicing, resulting in small amounts of functional protein still being produced. Therefore, we constructed a cDNA coding for the newly identified CYP3A5.11 protein by site-directed mutagenesis, expressed it in Escherichia coli, and partially purified it. Whereas bacteria transformed with wild-type CYP3A51 cDNA expressed predominantly cytochrome P450 (P450), those transfected with CYP3A511 expressed a significant amount of denatured cytochrome P420 in addition to P450, suggesting the protein to be unstable. CYP3A5.11 exhibited a 38% decrease in the V(max) for nifedipine metabolism, a 2.7-fold increase in the K(m), and a 4.4-fold decrease in the CL(int) of nifedipine compared with CYP3A5.1. A polymerase chain reaction-restriction fragment length polymorphism genotyping procedure was developed and used to genotype DNA of 500 white individuals for CYP3A511. No additional examples of this allele were identified. In summary, individuals carrying the rare CYP3A511 allele are predicted to have lower metabolism of CYP3A5 substrates than individuals expressing CYP3A5*3.