The “outsized” role of the I‐helix kink in human Cytochrome P450s

Abstract

Dear Editor, Cytochrome P450s (CYPs) are a superfamily of hemecontaining enzymes that play critical roles in oxidizing endogenous metabolites and xenobiotics. 1 They are membrane-anchored enzymes, and the transmembrane domains are involved in the electron transfer and the access of substrate and water during the catalytic cycle. [2][3][4] Mutations of human CYPs cause metabolic disorders and abnormal drug metabolism. 5 Because their amino acid sequences are remarkably diverse, the existing work on different human CYPs is seemingly unrelated. However, it is important to note that the overall structural folds of CYPs are largely conserved. 6 We, therefore, wondered if there is any shared feature of functionally unrelated human CYPs that is linked to enzyme malfunction and human disorders.The oxygen-binding motif is relatively conserved among different CPYs (Figure 1A), which locates in the central region of the I-helix and is implicated in the delivery of protons from water molecules to bound dioxygen during the catalytic cycle. [6][7][8][9] Interestingly, a closer examination of a few unrelated CYP structures revealed that the first two amino acids of the oxygen-binding motif produce a kink in the I-helix 6 (Figure 1B). Previous studies showed that mutations of this kink in CYP21A2 (G292S/C/R/D) and CYP11B1 (G314R) disrupt the biosynthesis of cortisol and aldosterone and lead to inherited congenital adrenal hyperplasia. 10,11 Because the kink is in close proximity with the oxidized moiety of the substrate and the heme iron, we hypothesized that the amino acid composition might be crucial to shaping the enzyme pocket environment, and changes could have a profound impact on enzyme activity for all CYPs. Interestingly, we found 84 nonsynonymous single-nucleotide polymorphisms (SNPs) in this kink region of human CYPs from the NCBI database of genetic variation (dbSNP), most of which remained uncharacterized (coloured in blue, Figure 1C; Table S1). Among them, only four, including G292R/S of CYP21A2, 10 G314R of CYP11B1 11 and G312R of CYP2J2, 12 have beenThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.