nuc_hydro_IU_UC_XIUA: inosine-uridine preferring, xanthosine-inosine-uridine-adenosine-preferring and, uridine-cytidine preferring nucleoside hydrolases. Nucleoside hydrolases cleave the N-glycosidic bond in nucleosides generating ribose and the respective base. These enzymes vary in their substrate specificity. This group contains proteins similar to nucleoside hydrolases which hydrolyze both pyrimidine and purine ribonucleosides: the inosine-uridine preferring nucleoside hydrolase from Crithidia fasciculata, the inosine-uridine-xanthosine preferring nucleoside hydrolase RihC from Escherichia coli and the xanthosine-inosine-uridine-adenosine-preferring nucleoside hydrolase RihC from Salmonella enterica serovar Typhimurium. This group also contains proteins similar to the pyrimidine-specific uridine-cytidine preferring nucleoside hydrolases URH1 from Saccharomyces cerevisiae, E. coli RihA and E. coli RihB. E. coli RihA is equally efficient with uridine and cytidine, E. coli RihB prefers cytidine over uridine. S. cerevisiae URH1 prefers uridine over cytidine.
Comment:2MAS_A, PDB D10 is the proposed general base in the general acid catalysis
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:This group of nucleoside hydrolases possesses a histidine or a tyrosine residue at a position equivalent to the catalytic histidine241 in the inosine-uridine-preferring nucleoside hydrolase of C. fasciculata.
Jiyao W et al.(2023). "The conserved domain database in 2023.",