Site-directed mutagenesis studies of acetylglutamate synthase delineate the site for the arginine inhibitor

N-acetyl-l-glutamate synthase (NAGS), the first enzyme of bacterial/plant arginine biosynthesis and an essential activator of the urea cycle in animals, is, respectively, arginine-inhibited and activated. Site-directed mutagenesis of recombinant Pseudomonas aeruginosa NAGS (PaNAGS) delineates the arginine site in the PaNAGS acetylglutamate kinase-like domain, and, by extension, in human NAGS. Key residues for glutamate binding are identified in the acetyltransferase domain. However, the acetylglutamate kinase-like domain may modulate glutamate binding, since one mutation affecting this domain increases the Km for glutamate. The effects on PaNAGS of two mutations found in human NAGS deficiency support the similarity of bacterial and human NAGSs despite their low sequence identity.