Azole resistance: patterns of amino acid substitutions in Candida sterol 14α-demethylase

The emergence of azole-resistant Candida infections is a major concern. A key mechanism is the gain of resistance through amino acid substitutions in the sterol 14α-demethylase, the main target of azole drugs. While numerous resistant substitutions are known, the pattern of such substitutions remains unclear. We hypothesized that resistant substitutions occur disproportionately at azole-binding sites. We compiled 2222 instances of azole-resistant substitutions from the literature and performed extensive computational sequence analyses. Altogether, there were 169 known substitutions at 133 sites in sterol 14α-demethylases of seven Candida species, whereas C. albicans alone had 120 substitutions at 97 sites. Just 10 sites and 18 substitutions (such as Y132F/H, K143R, D116E, and G464S) accounted for 75% of the total instances. Only about 48% of the sites were present within previously recognized hotspot regions, while just 33% of the azole-interacting residues had known resistant substitutions, most of them with only a few instances. The literature data on azole-resistant substitutions in Candida appear to be highly biased, as a few substitutions, such as Y132F/H and K143R, were preferentially sought and reported with over 1,000 instances. Additionally, there were numerous reports of "resistant" substitutions in azole-susceptible Candida isolates. Our study provides new perspectives into azole resistance.