title: Identification, cloning and expression of the mouse N-acetylglutamate synthase gene.
abstract: In ureotelic animals, N-acetylglutamate (NAG) is an essential allosteric activator of carbamylphosphate synthetase I (CPSI), the first enzyme in the urea cycle. NAG synthase (NAGS; EC 2.3.1.1) catalyses the formation of NAG from glutamate and acetyl-CoA in liver and intestinal mitochondria. This enzyme is supposed to regulate ureagenesis by producing variable amounts of NAG, thus modulating CPSI activity. Moreover, inherited deficiencies in NAGS have been associated with hyperammonaemia, probably due to the loss of CPSI activity. Although the existence of the NAGS protein in mammals has been known for decades, the gene has remained elusive. We identified the mouse (Mus musculus) and human NAGS genes using their similarity to the respective Neurospora crassa gene. NAGS was cloned from a mouse liver cDNA library and was found to encode a 2.3 kb message, highly expressed in liver and small intestine with lower expression levels in kidney, spleen and testis. The deduced amino acid sequence contains a putative mitochondrial targeting signal at the N-terminus. The cDNA sequence complements an argA (NAGS)-deficient Escherichia coli strain, reversing its arginine auxotrophy. His-tagged versions of the pre-protein and two putative mature proteins were each overexpressed in E. coli, and purified to apparent homogeneity by using a nickel-affinity column. The pre-protein and the two putative mature proteins catalysed the NAGS reaction but one of the putative mature enzymes had significantly higher activity than the pre-protein. The addition of l-arginine increased the catalytic activity of the purified recombinant NAGS enzymes by approx. 2-6-fold.
authors.affiliation: Children's Research Institute, Children's National Medical Center, George Washington University, 111 Michigan Ave NW, Washington, DC 20010, USA.
authors.forename: Ljubica
authors.initials: L
authors.lastname: Caldovic
authors.forename: Hiroki
authors.initials: H
authors.lastname: Morizono
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Yu
authors.forename: Mark
authors.initials: M
authors.lastname: Thompson
authors.forename: Dashuang
authors.initials: D
authors.lastname: Shi
authors.forename: Rene
authors.initials: R
authors.lastname: Gallegos
authors.forename: Norma M
authors.initials: NM
authors.lastname: Allewell
authors.forename: Michael H
authors.initials: MH
authors.lastname: Malamy
authors.forename: Mendel
authors.initials: M
authors.lastname: Tuchman
mesh_terms: D000123:Acetyltransferases / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D051046:Amino-Acid N-Acetyltransferase; D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004926:Escherichia coli / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D005816:Genetic Complementation Test; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000201:enzymology; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D012568:Schizosaccharomyces / Q000201:enzymology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; D011994:Recombinant Proteins; D000123:Acetyltransferases; D051046:Amino-Acid N-Acetyltransferase; C494877:Nags protein, mouse