Structure of the DNA-binding domain of the response regulator SaeR from Staphylococcus aureus

The SaeR/S two-component regulatory system is essential for controlling the expression of many virulence factors in Staphylococcus aureus. SaeR, a member of the OmpR/PhoB family, is a response regulator with an N-terminal regulatory domain and a C-terminal DNA-binding domain. In order to elucidate how SaeR binds to the promoter regions of target genes, the crystal structure of the DNA-binding domain of SaeR (SaeR(DBD)) was solved at 2.5 angstrom resolution. The structure reveals that SaeR(DBD) exists as a monomer and has the canonical winged helix-turn-helix module. EMSA experiments suggested that full-length SaeR can bind to the P1 promoter and that the binding affinity is higher than that of its C-terminal DNA-binding domain. Five key residues on the winged helix-turn-helix module were verified to be important for binding to the P1 promoter in vitro and for the physiological function of SaeR in vivo.