The rs35217482 (T755I) Single-Nucleotide Polymorphism in Aldehyde Oxidase-1 Attenuates Protein Dimer Formation and Reduces the Rates of Phthalazine MetabolismS

Abstract

Aldehyde oxidase-1 (AOX1) is a molybdenum-containing enzyme that catalyzes the oxidation of a range of aldehyde compounds and clinical drugs, including azathioprine and methotrexate. The purpose of this study was to elucidate the effects of single-nucleotide polymorphisms (SNPs) in the coding regions of the human AOX1 gene on protein dimer formation and metabolic activity. Six variants [Q314R (rs58185012), I598N (rs143935618), T755I (rs35217482), A1083G (rs139092129), N1135S (rs55754655), and H1297R (rs3731722)], with allele frequencies greater than 0.01 in 1 or more population, were obtained from the genome aggregation and 1000 Genomes Project databases. Protein expression and dimer formation were evaluated using HEK293T cells expressing the wild-type (WT) or different SNP variants of AOX1. Kinetic analyses of phthalazine oxidation were performed using S9 fractions of HEK293T cells expressing WT or each the different mutant AOX1. Although we detected no significant differences among WT AOX1 and the different variants with respect to total protein expression, native PAGE analysis indicated that one of the SNP variants, T755I, found in East Asian populations, dimerizes less efficiently than the WT AOX1. Kinetic analysis, using phthalazine as a typical substrate, revealed that this mutation contributes to a reduction in the maximal rates of reaction without affecting enzyme affinity for phthalazine. Our observation thus indicates that the T755I variant has significantly negative effects on both the dimer formation and in vitro catalytic activity of AOX1. These findings may provide valuable insights into the mechanisms underlying the interindividual differences in the therapeutic efficacy or toxicity of AOX1 substrate drugs.