NH_hydro_CaPnhB: A subgroup of nucleoside hydrolases similar to Corynebacterium ammoniagenes Purine/pyrimidine nucleoside hydrolase (pnhB). Nucleoside hydrolases cleave the N-glycosidic bond in nucleosides generating ribose and the respective base. These enzymes vary in their substrate specificity.
Comment:Most nucleoside hydrolases possess either a tryptophan or a histidine at a position equivalent to PDB H241 in the base-aspecific nucleoside hydrolase of Crithidia fasciculate (2MAS_A). This histidine has been identified as the general acid in the catalysis. In the nucleoside hydrolase of the parasite Trypanosoma vivax (1HP0_A), as an alternative to general acid catalysis, the purine base of the substrate is bound between the aromatic side chains of W83 and W260, promoting the protonation of the purine base at N-7.
Comment:The majority of this group of nucleoside hydrolases possess a histidine, at a position equivalent to gi48762773, loc234; the inosine-uridine-preferring nucleoside hydrolase of Crithidia fasciculata has a catalytic histidine (H241)at this position.
Jiyao W et al.(2023). "The conserved domain database in 2023.",