title: Evaluation of NAD(+) -dependent DNA ligase of mycobacteria as a potential target for antibiotics.
abstract: Mycobacteria contain genes for several DNA ligases, including ligA, which encodes a NAD(+)-dependent enzyme that has been postulated to be a target for novel antibacterial compounds. Using a homologous recombination system, direct evidence is presented that wild-type ligA cannot be deleted from the chromosome of Mycobacterium smegmatis. Deletions of native ligA in M. smegmatis could be obtained only after the integration of an extra copy of M. smegmatis or Mycobacterium tuberculosis ligA into the attB site of the chromosome, with expression controlled by chemically inducible promoters. The four ATP-dependent DNA ligases encoded by the M. smegmatis chromosome were unable to replace the function of LigA. Interestingly, the LigA protein from M. smegmatis could be substituted with the NAD(+)-dependent DNA ligase of Escherichia coli or the ATP-dependent ligase of bacteriophage T4. The conditional mutant strains allowed the analysis of the effect of LigA depletion on the growth of M. smegmatis. The protein level of the conditional mutants was estimated by Western blot analysis using antibodies raised against LigA of M. tuberculosis. This revealed that a strong overproduction or depletion of LigA did not affect the growth or survival of mycobacteria under standard laboratory conditions. In conclusion, although NAD(+)-dependent DNA ligase is essential for mycobacterial viability, only low levels of protein are required for growth. These findings suggest that very efficient inhibition of enzyme activity would be required if NAD(+)-dependent DNA ligase is to be useful as an antibiotic target in mycobacteria. The strains developed here will provide useful tools for the evaluation of the efficacy of any appropriate compounds in mycobacteria.
authors.affiliation: Centre of Medical Biology, Polish Academy of Sciences, Lodowa 106, Lodz, Poland.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Korycka-Machala
authors.forename: Ewelina
authors.initials: E
authors.lastname: Rychta
authors.forename: Anna
authors.initials: A
authors.lastname: Brzostek
authors.forename: Heather R
authors.initials: HR
authors.lastname: Sayer
authors.forename: Anna
authors.initials: A
authors.lastname: Rumijowska-Galewicz
authors.forename: Richard P
authors.initials: RP
authors.lastname: Bowater
authors.forename: Jarosław
authors.initials: J
authors.lastname: Dziadek
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D011088:DNA Ligases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D005818:Genetic Engineering / Q000379:methods; D006801:Humans; D009154:Mutation; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development; D009243:NAD / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D009243:NAD; D011088:DNA Ligases; C120640:DNA ligase (NAD); C497118:LigA protein, E coli