This invention relates to recombinant DNA technology. In particular the invention pertains to the cloning of a gene, mtg, encoding a novel monofunctional glycosyltransferase, from Staphylococcus aureus and the use of said gene and its encoded protein in a screen for new inhibitors of bacterial cell wall biosynthesis.
The emergence of antibiotic resistance in common pathogenic bacterial species has justifiably alarmed the medical and research communities. The emergence and rapid spread of beta-lactam resistance has been particularly problematic. Increasingly, the only drug that can be used to treat infections with MDR (multiple drug resistant) organisms is vancomycin, and there is considerable concern that the bacteria could also develop resistance to vancomycin.
The bacterial cell wall comprises a peptidoglycan layer which provides mechanical rigidity for the bacterium. The peptidoglycan layer is composed of a sugar backbone (alternating residues of N-acetylglucosamine and N-acetylmuramic acid are polymerized through a transglycosylation reaction) attached to a pentapeptide (also referred to as "stem peptide") containing D and L amino acid residues. Adjacent stem peptide residues are covalently crosslinked during maturation of the peptidoglycan.
During formation of the mature peptidoglycan, a lipid-linked disaccharide-pentapeptide is translocated across the cytoplasmic membrane, exposing the pentapeptide sidechains to the cell surface. The fully mature peptidoglycan structure is obtained following transglycosylation and transpeptidation enzymatic reactions. Several enzymes appear to be involved in the transglycosylation and transpeptidation polymerizaion reactions, most notably the bifunctional high molecular weight PBPs. Interestingly, transglycosylation activity is also found in monofunctional enzymes known as monofunctional glycosyltransferases (MTG's). The MTG is a target for the development of new inhibitors of cell wall synthesis.