species have a lysine residue at this position. This cysteine is located in the flexible loop, which prevents the physiological substrate from binding. Mechanism The catalytic mechanism for NagA enzymes proposed utilizes nucleophilic attack via a metal-coordinated water molecule or hydroxide ion. The mechanism proceeds via a strictly conserved active-site aspartic acid residue (Asp-273) that acts initially as a base to activate the hydrolytic water molecule in order to attack the carbonyl group of the substrate. Asp-273 then acts as an acid to protonate the amine leaving group. One proposed mechanism using the BsNagA and its two iron co-factors in the metal-binding site demonstrates the nucleophilic attack by an Fe-bridged hydroxide and then the stabilization of the carbonyl oxygen by one of the two Fe atoms. Biological Function NagA is located in the cytoplasm of the cell. N-acetylglucosamine (GlcNAc) enters the cell as part of the breakdown of the cell wall. GlcNAc, a monosaccharide and derivative of glucose, is part of a biopolymer in the bacterial cell wall. This biopolymer forms a layered structure called peptidoglycan (PG). GlcNAc is then converted into GlcNAc-6-P by the enzyme NagE. This substrate is then deacetylated into acetate and GlcN-6-P by NagA. NagA is important for the production of GlcN-6-P, which is then used in two main pathways: PG recycling pathway and the glycolysis pathway. PG recycling pathway In the PG Recycling pathway, once GlcNAc-6-P is metabolized by NagA, its product, GlcN-6-P, can then be converted to GlcN-1-P by the enzyme GlmM, followed by reacetylation and reaction with UTP by GlmU to form UDP-GlcNAc. UDP-GlcNAc is the end product of this pathway, which is then used to make glycosaminoglycans, proteoglycans, and glycolipids, which are all necessary in order to replenish PG for the cell wall. PG recycling is necessary for bacterial cells in order to ensure bacteria growth and prevent cell lysis. Glycolysis pathway Instead of entering the PG recycling pathway, GlcN-6-P can be converted into fructose-6-phosphate by NagB. This reaction is reversible by the enzyme GlmS, an amidotransferase. The produced fructose-6-phosphate then enters the glycolysis pathway. Glycolysis catalyzes the production of pyruvate, leading to the citric acid cycle and allowing for the production of amino acids. GlcN-6-P and fructose-6-phosphate act as allosteric regulators of NagA, inhibiting further deacetylation of GlcNAc-6-P. Disease relevance NagA is a potential drug target of Mycobacterium tuberculosis (Mtb). Eliminating NagA produces high levels of the allosteric activator GlcNAc-6-P, which