, 1957; Girodeau et al., 1986; Lloyd et al., 2004). Attempts to express the Mt-dapF (Rv 2726c) in E. coli failed, in spite of the highly efficient T7 promoter in the pET28 vector. It was reasoned out that the lack of dapF expression was related to poor translation (Usha et al., 2006). Mt-dapF was subsequently cloned and over-expressed using a novel codon

alteration strategy and the purified recombinant enzyme functionally characterized (Usha et al., 2006). The Km for meso-DAP was determined to be 1217 μM. Mt-DapF exists as a monomer. Dithiothreitol is required for Mt-DapF activity, consistent with its requirement for two reduced active site thiols (Usha et al., 2006). Mt-DapF activity is inactivated in the presence of nanomolar selleck inhibitor concentrations of the three different thiol-specific alkylating agents (Usha et al., 2008). Site-directed mutagenesis confirmed that the two conserved Cys87 and Cys226 residues were involved in catalysis (Usha et al., 2008). The crystal structure of

the unliganded form of Mt-DapF has been refined to 2.6 Ǻ resolution. Mt-DapF is made up of two pseudosymmetrical α/β domains (Usha et al., 2009). The active site is located in the cleft between domains I and II. The ribbon model of Mt-DapF learn more is shown in Fig. 2. Tyr76 is unique to suborder Corynebacterineae DapF, suggesting a route to the design of a species-specific inhibitor (Usha et al., 2009). In mycobacteria, and most Gram-negative bacteria, the third residue in the peptidoglycan (PG) pentapeptide is d,l (meso)-diaminopimelic acid (Schleifer

& Kandler, 1972). During exponential phase, mycobacteria cross-link the third (meso-DAP) residue and the fourth (d-Ala) residue of adjacent stem peptides (Schleifer & Kandler, 1972; Wietzerbin et al., 1974). On entering stationary phase, mycobacteria incorporate increasing amounts of meso-DAPmeso-DAP linkages, which results in an unusually high DAP content (Wietzerbin et al., 1974; Cirillo et al., 1994a). meso-DAP next is essential for both types of mycobacterial PG cross-linking. The percentage of cross-linking is very high (70–80%) in Mycobacterium species compared to E. coli (20–30%) (Cirillo et al., 1994b; Matsuhashi, 1994). meso-DAP is introduced into the PG network as part of the cross-linking moiety between the polysaccharide fibres (Ghuysen, 1980) (Fig. 3). In addition, the synthesis of meso-DAP is required for protein synthesis, because after decarboxylation, it yields l-lysine. Orthologues in M. tuberculosis of most of the DAP biosynthesis enzymes have been stably expressed in soluble form and functionally characterized. The crystal structures of most of the DAP biosynthesis enzymes have been solved and the chemical mechanisms studied.