The 5023A>G SNP, results in an amino acid change tyrosine to histidine at position 351 (Y351H), predicted as ‘damaging’ by SIFT [28]and ‘probably damaging’ with a score of 1.0 by PolyPhen [29]. In the CYP2A6 crystal structure, the hydroxyl of Tyr351 interacts with a water molecule that bridges between this residue, Lys326 and Gln414. All three residues are on the surface of the protein, more than 25 angstroms away from the iron, and on the opposite side of the heme from the active site[30]. However, alteration of the residue at 351 might indirectly affect protein stability or heme coordination. The five amino acid changes in the other two individuals are predicted as ‘tolerated’ by SIFT and ‘benign’ by PolyPhen. However, two of these changes N418D and E419D, occur together in the CYP2A6*28 allele, reported to display significantly impaired enzymatic activity [31]. This allele has been previously reported only in subjects of African descent [31]. Eigenstrat analysis, however, confirmed that the individual in our study falls within the European cluster. The K476R change defines the CYP2A6*21 allele, reported in Europeans[32], and was previously reported to not significantly alter the activity of CYP2A6 in vivo [32].
