Sulfonamide Inhibition Studies of the β-Class Carbonic Anhydrase CAS3 from the Filamentous Ascomycete Sordaria macrospora

A new β-class Carbonic Anhydrase was cloned and purified from the filamentous ascomycete Sordaria macrospora, CAS3. This Enzyme has a higher catalytic activity compared to the other two such enzymes from this fungus, CAS1 and CAS2, which were reported earlier, with the following kinetic parameters: k_cat of (7.9 ± 0.2) × 10⁵ s^-1, and k_cat/K_m of (9.5 ± 0.12) × 10⁷ M^-1∙s^-1. An inhibition study with a panel of sulfonamides and one sulfamate was also performed. The most effective CAS3 inhibitors were benzolamide, brinzolamide, dichlorophnamide, methazolamide, acetazolamide, ethoxzolamide, sulfanilamide, methanilamide, and benzene-1,3-disulfonamide, with K_Is in the range of 54-95 nM. CAS3 generally shows a higher affinity for this class of inhibitors compared to CAS1 and CAS2. As S. macrospora is a model organism for the study of fruiting body development in fungi, these data may be useful for developing Antifungal compounds based on CA inhibition.