Structural insights into the substrate binding mechanism of novel ArgA from Mycobacterium tuberculosis

Abstract The Mycobacterium tuberculosis (Mtb) Rv2747 gene encodes for a functional protein known as ArgA, which plays an important role in the first step of the l -arginine biosynthesis pathway. ArgA transfers the acetyl group from the acetyl-CoA to either l -glutamate or l -glutamine, which are the known substrates. Here, we present two crystal structures of ArgA: one complexed with CoA and product bound N- acetylglutamine and the other complexed with acetyl-CoA and the inhibitor l -arginine at 2.3 and 3.0 A resolution respectively. The Mtb ArgA protomer was found to have a “V” cleft and a “β” bulge, archetypal of a classical GCN5-related N -acetyltransferase superfamily of proteins. The product bound form implies that ArgA can also acetylate l -glutamine like l -glutamate. The active site is strongly inhibited by l -arginine resulting in a closed conformation of ArgA and both l -arginine and N- acetylglutamine were found to occupy at the same active site. Together with structural analysis, molecular docking studies, microscale thermophoresis and enzyme inhibition assays, we conclude that l -glutamine, l -glutamate and l -arginine, all occupy at the same active site of ArgA. Furthermore in case of Mtb ArgA, l -arginine does not act as an allosteric inhibitor unlike other N -acetylglutamate synthase family of proteins.