Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
The crystal structure of GMP synthetase serves as a prototype for two families of metabolic enzymes. The Class I glutamine amidotransferase domain of GMP synthetase is found in related enzymes of the purine, pyrimidine, tryptophan, arginine, histidine and folic acid biosynthetic pathways. This domain includes a conserved Cys-His-Glu triad and is representative of a new family of enzymes that use a catalytic triad for enzymatic hydrolysis. The structure and conserved sequence fingerprint of the nucleotide-binding site in a second domain of GMP synthetase are common to a family of ATP pyrophosphatases, including NAD synthetase, asparagine synthetase and argininosuccinate synthetase.