The signature amidase from Sulfolobus solfataricus belongs to the CX3C subgroup of enzymes cleaving both amides and nitriles. Ser195 and Cys145 are predicted to be the active site nucleophiles.

The signature amidase from the extremophile archeum Sulfolobus solfataricus is an enantioselective enzyme that cleaves S-amides. We report here that this enzyme also converts nitriles in the corresponding organic acid, similarly to the well characterized amidase from Rhodococcus rhodochrous J1. The archaeal and rhodococcal enzymes belong to the signature amidases and contain the typical serine-glycine rich motif.