Identification of a hydrophobic cleft in the LytTR domain of AgrA as a locus for small molecule interactions that inhibit DNA binding.

The AgrA transcription factor regulates the quorum-sensing response in Staphylococcus aureus, controlling the production of hemolysins and other virulence factors. AgrA binds to DNA via its C-terminal LytTR domain, a domain not found in humans but common in many pathogenic bacteria, making it a potential target for antimicrobial development. We have determined the crystal structure of the apo AgrA LytTR domain and screened a library of 500 fragment compounds to find inhibitors of AgrA DNA binding activity. Using nuclear magnetic resonance, the binding site for five compounds has been mapped to a common locus at the C-terminal end of the LytTR domain, a site known to be important for DNA binding activity. Three of these compounds inhibit AgrA DNA binding. These results provide the first evidence that LytTR domains can be targeted by small organic compounds.