Mutation analysis of carbamoyl phosphate synthetase: does the structurally conserved glutamine amidotransferase triad act as a functional dyad?

ABSTRACT: Evolutionarily conserved triad glutamine amidotransferase (GAT) domains catalyze the cleavage of glutamine to yield ammonia and sequester the ammonia in a tunnel until delivery to a variety of acceptor substrates in synthetase domains of variable structure. Whereas a conserved hydrolytic triad (Cys/His/Glu) is observed in the solved GAT structures, the specificity pocket for glutamine is not apparent, presumably because its formation is dependent on the conformational change that couples acceptor availability to a greatly increased rate of glutamine cleavage. In Escherichia coli carbamoyl phosphate synthetase (eCPS), one of the best characterized triad GAT members, the Cys269 and His353 triad residues are essential for glutamine hydrolysis, whereas Glu355 is not critical for eCPS activity.

SUBMITTER: Hart EJ 

PROVIDER: S-EPMC2442002 | biostudies-literature | 2008 Jul

REPOSITORIES: biostudies-literature