Mechanism of Allosteric Inhibition of N-Acetyl-L-glutamate Synthase by L-Arginine

• Published in: The Journal of biological chemistry Vol. 284; no. 8; pp. 4873 - 4880
• Main Authors: Min, Li, Jin, Zhongmin, Caldovic, Ljubica, Morizono, Hiroki, Allewell, Norma M., Tuchman, Mendel, Shi, Dashuang
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 20-02-2009; American Society for Biochemistry and Molecular Biology
• Subjects: Allosteric Regulation - physiology; AMINO ACIDS; Amino-Acid N-Acetyltransferase - antagonists & inhibitors; Amino-Acid N-Acetyltransferase - chemistry; Amino-Acid N-Acetyltransferase - metabolism; Arginine - chemistry; Arginine - metabolism; Bacterial Proteins - antagonists & inhibitors; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; BIOSYNTHESIS; CONFORMATIONAL CHANGES; CRYSTAL STRUCTURE; Crystallography, X-Ray; Dimerization; DIMERS; Enzyme Catalysis and Regulation; ENZYMES; FEEDBACK; MATERIALS SCIENCE; MONOMERS; Neisseria gonorrhoeae; Neisseria gonorrhoeae - enzymology; PHOSPHOTRANSFERASES; Protein Structure, Quaternary - physiology; Protein Structure, Secondary - physiology; Protein Structure, Tertiary - physiology; PROTEINS; Structural Homology, Protein; TRANSFERASES
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M805348200

N-Acetylglutamate synthase (NAGS) catalyzes the first committed step in l-arginine biosynthesis in plants and micro-organisms and is subject to feedback inhibition by l-arginine. This study compares the crystal structures of NAGS from Neisseria gonorrhoeae (ngNAGS) in the inactive T-state with l-arginine bound and in the active R-state complexed with CoA and l-glutamate. Under all of the conditions examined, the enzyme consists of two stacked trimers. Each monomer has two domains: an amino acid kinase (AAK) domain with an AAK-like fold but lacking kinase activity and an N-acetyltransferase (NAT) domain homologous to other GCN5-related transferases. Binding of l-arginine to the AAK domain induces a global conformational change that increases the diameter of the hexamer by ∼10 Å and decreases its height by ∼20Å. AAK dimers move 5Å outward along their 2-fold axes, and their tilt relative to the plane of the hexamer decreases by ∼4°. The NAT domains rotate ∼109° relative to AAK domains enabling new interdomain interactions. Interactions between AAK and NAT domains on different subunits also change. Local motions of several loops at the l-arginine-binding site enable the protein to close around the bound ligand, whereas several loops at the NAT active site become disordered, markedly reducing enzymatic specific activity.