We are very grateful to Ms. María Isabel Bernal for her excellent technical assistance. This work was supported in part by grants from Agencia Nacional de Promoción a la Ciencia y Tecnología (PICT 2006-00407) and from Universidad de Buenos Aires (UBACyT 2002 00903 0028 y M009), Argentina. “
“Bioscience Division, Los Alamos National Laboratory, this website Los Alamos, NM, USA InStem, National Centre for Biological Sciences, Bangalore, India Southern Illinois University School of Medicine, Carbondale, IL, USA The Mycobacterium tuberculosis murG gene, Rv2153, was expressed in Escherichia

coli murG(Ts) strain OV58 on a plasmid under the control of the arabinose-inducible araBAD promoter. Mycobacterium tuberculosis murG rescued the growth of E. coli murG(Ts) LGK-974 mouse at the nonpermissive temperature: transformants were only obtained in the presence of 0.2% arabinose at 42 °C, and their growth rate was dependent on arabinose concentrations. However, no MurG activity was detected in membranes from the transformant grown in arabinose at 42 °C, while MraY

activity was normal. This observation led to the development of a membrane-based scintillation proximity assay for exogenous sources of MurG. Addition of purified E. coli MurG resulted in the reconstitution of MurG and peptidoglycan synthesis in these membranes. MurG is an attractive target for drug discovery, but assays to measure the activity of purified MurG are challenging. This presents an easy method to measure the activity of exogenous sources of MurG for structure–activity studies PtdIns(3,4)P2 of mutant MurG proteins. It can also be used to compare the activity of, or effect of inhibitors on, MurG from other bacterial species. There is an urgent need for new antibacterial agents to treat resistant bacterial infections (Boucher et al., 2009). Many successful drugs, for example the β-lactams and vancomycin, target enzymes in the peptidoglycan pathway. MurG, which catalyses an essential step of peptidoglycan synthesis, is an attractive target for both target-

and structure-based drug discovery, because crystal structures of MurG have been determined (Ha et al., 2000; Hu et al., 2003). MurG catalyses (Fig. 1a) the transfer of N-acetylglucosamine (GlcNAc) from UDP-GlcNAc to MurNAc-(pentapeptide)-pyrophosphoryl undecaprenol (lipid I) yielding GlcNAc-MurNAc(pentapeptide)-pyrophosphoryl undecaprenol (lipid II). However, measuring the activity of MurG during purification is challenging, as its substrate, lipid I, is not water soluble and is difficult to synthesize or isolate from bacteria in large quantities. The enzyme can either be assayed in its natural membrane environment (Mengin-Lecreulx et al., 1991) or in solution (Auger et al., 1997, 2003; Ha et al., 1999, 2000; Chen et al., 2002), although the synthetic substrates (Men et al., 1998; Auger et al., 1997, 2003; Ha et al., 1999, 2000; Chen et al., 2002) need considerable expertise to synthesize.