Crystal structure of l-glutamate N-acetyltransferase ArgA from Mycobacterium tuberculosis

Abstract l -arginine is used as a source of both carbon and nitrogen in Mycobacterium tuberculosis ( Mtb ) and its biosynthesis is essential for the pathogen's survival. Mtb ArgA (Rv2747) catalyzes the initial step in l -arginine biosynthesis by transferring an acetyl group from acetyl coenzyme A (AcCoA) to l -glutamate. Mtb ArgA is a class III N -acetylglutamate synthase (NAGS) with no structural information. Here, we solved the crystal structure of Mtb ArgA complexed with AcCoA and l -glutamate. The overall structure adopts a classic fold of the GCN5-related N -acetyltransferase (GNAT) family, characterized by a “V”-shaped cleft and β-bulge, but uses distinct residues for the binding and reaction of AcCoA. In particular, its activity depends on dimerization to form a deep, vast pocket for l -glutamate binding. Interestingly, in the structure, l -glutamate binds at a site far away from AcCoA, implying a mechanism of separate capture and catalysis. Additionally, based on a docking model of l -glutamate at the catalytic site, a one-step sequential mechanism was proposed for enzymatic catalysis. Important sites for substrate binding and catalysis were also evaluated by site-directed mutagenesis study and activity analysis. The unique features of the Mtb ArgA structure will provide useful insights for inhibitor design and anti-tuberculosis drug discovery.