Nitrilases, cyanide hydratase (CH)s, and similar proteins (class 1 nitrilases)
Nitrilases (nitrile aminohydrolases, EC:3.5.5.1) hydrolyze nitriles (RCN) to ammonia and the corresponding carboxylic acid. Most nitrilases prefer aromatic nitriles, some prefer arylacetonitriles and others aliphatic nitriles. This group includes the nitrilase cyanide dihydratase (CDH), which hydrolyzes inorganic cyanide (HCN) to produce formate. It also includes cyanide hydratase (CH), which hydrolyzes HCN to formamide. This group includes four Arabidopsis thaliana nitrilases (Ath)NIT1-4. AthNIT1-3 have a strong substrate preference for phenylpropionitrile (PPN) and other nitriles which may originate from the breakdown of glucosinolates. The product of PPN hydrolysis, phenylacetic acid has auxin activity. AthNIT1-3 can also convert indoacetonitrile to indole-3-acetic acid (IAA, auxin), but with a lower affinity and velocity. From their expression patterns, it has been speculated that NIT3 may produce IAA during the early stages of germination, and that NIT3 may produce IAA during embryo development and maturation. AthNIT4 has a strong substrate specificity for the nitrile, beta-cyano-L-alanine (Ala(CN)), an intermediate of cyanide detoxification. AthNIT4 has both a nitrilase activity and a nitrile hydratase (NHase) activity, which generate aspartic acid and asparagine respectively from Ala(CN). NHase catalyzes the hydration of nitriles to their corresponding amides. This subgroup belongs to a larger nitrilase superfamily comprised of belong to a larger nitrilase superfamily comprised of nitrile- or amide-hydrolyzing enzymes and amide-condensing enzymes, which depend on a Glu-Lys-Cys catalytic triad. This superfamily has been classified in the literature based on global and structure based sequence analysis into thirteen different enzyme classes (referred to as 1-13), this subgroup corresponds to class 1.
Jiyao W et al.(2023). "The conserved domain database in 2023.",