The N-acetylmannosamine transferase catalyzes the first committed step of teichoic acid assembly in Bacillus subtilis and Staphylococcus aureus

The wall teichoic acid and lipoteichoic acid polymers of Staphylococcus aureus

Staphylococci and most other Gram-positive bacteria incorporate complex teichoic acid (TA) polymers into their cell envelopes. Several crucial roles in Staphylococcus aureus fitness and cell wall maintenance have been assigned to these polymers, which are either covalently linked to peptidoglycan (wall teichoic acid, WTA) or to the cytoplasmic membrane (lipoteichoic acid, LTA). However, the exact TA structures, functions, and biosynthetic pathways are only superficially understood. Recently, most of the enzymes mediating TA biosynthesis have been identified and mutants lacking or with defined changes in WTA or LTA have become available. Their characterization has revealed crucial roles of TAs in protection against harmful molecules and environmental stresses; in control of enzymes directing cell division or morphogenesis and of cation homeostasis; and in interaction with host or bacteriophage receptors and biomaterials. Accordingly, several in vivo studies have demonstrated the importance of WTA and LTA in S. aureus colonization, infection, and immune evasion. TAs and enzymes required for TA biosynthesis represent attractive candidates for novel vaccines and antibiotics and are targeted by recently developed antibacterial therapeutics.

Discovery of a small molecule that blocks wall teichoic acid biosynthesis in Staphylococcus aureus

Both Gram-positive and Gram-negative bacteria contain bactoprenol-dependent biosynthetic pathways expressing non-essential cell surface polysaccharides that function as virulence factors. Although these polymers are not required for bacterial viability in vitro, genes in many of the biosynthetic pathways are conditionally essential: they cannot be deleted except in strains incapable of initiating polymer synthesis. We report a cell-based, pathway-specific strategy to screen for small molecule inhibitors of conditionally essential enzymes. The screen identifies molecules that prevent the growth of a wildtype bacterial strain but do not affect the growth of a mutant strain incapable of initiating polymer synthesis. We have applied this approach to discover inhibitors of wall teichoic acid (WTA) biosynthesis in Staphylococcus aureus. WTAs are anionic cell surface polysaccharides required for host colonization that have been suggested as targets for new antimicrobials. We have identified a small molecule, 7-chloro-N,N-diethyl-3-(phenylsulfonyl)-[1,2,3]triazolo[1,5-a]quinolin-5-amine (1835F03), that inhibits the growth of a panel of S. aureus strains (MIC = 1-3 microg mL(-1)), including clinical methicillin-resistant S. aureus (MRSA) isolates. Using a combination of biochemistry and genetics, we have identified the molecular target as TarG, the transmembrane component of the ABC transporter that exports WTAs to the cell surface. We also show that preventing the completion of WTA biosynthesis once it has been initiated triggers growth arrest. The discovery of 1835F03 validates our chemical genetics strategy for identifying inhibitors of conditionally essential enzymes, and the strategy should be applicable to many other bactoprenol-dependent biosynthetic pathways in the pursuit of novel antibacterials and probes of bacterial stress responses.