Inosine-uridine preferring nucleoside hydrolase (3.2.2.1) (IU-nucleoside hydrolase or IUNH) is an enzyme first identified in protozoan [1] that catalyses the hydrolysis of all of the commonly occuring purine and pyrimidine nucleosides into ribose and the associated base, but has a preference for inosine and uridine as substrates. This enzyme is important for these parasitic organisms, which are deficient in de novo synthesis of purines, to salvage the host purine nucleosides. IUNH from Crithidia fasciculata has been sequenced and characterised, it is an homotetrameric enzyme of subunits of 34 Kd. An histidine has been shown to be important for the catalytic mechanism, it acts as a proton donor to activate the hypoxanthine leaving group.

A highly conserved region located in the N-terminal extremity contains four conserved aspartates that have been shown [2] to be located in the active site cavity.

IUNH is evolutionary related to a number of uncharacterised proteins from various biological sources.

1. Inosine-uridine nucleoside hydrolase from Crithidia fasciculata. Genetic characterization, crystallization, and identification of histidine 241 as a catalytic site residue. Biochemistry 35, 5963-70
2. Three-dimensional structure of the inosine-uridine nucleoside N-ribohydrolase from Crithidia fasciculata. Biochemistry 35, 5971-81

Inosine-uridine preferring nucleoside hydrolase (Show more...

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