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 14-demethylase, the main target of azole drugs. While numerous resistant substitutions are known, the pattern of such substitutions is unclear. We hypothesized that the resistant substitutions occur disproportionately at the azole-binding sites. We compiled 2,222 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 14-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 the previously recognized hotspot regions, while just 33% of the known 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 1000 instances, while there were also numerous reports of "resistant" substitutions in azole-susceptible Candida isolates. Our study provides interesting perspectives into azole resistance.