Identification and Physicochemical Characterization of BldR2 from Sulfolobus solfataricus, a Novel Archaeal Member of the MarR Transcription Factor Family

The multiple antibiotic resistance regulators (MarR) constitute a family of ligand-responsive transcriptional regulators abundantly distributed throughout the bacterial and archaeal domains. Here we describe the identification and characterization of BldR2, as a new member of this family, in the archaeon Sulfolobus solfataricus and report physiological, biochemical, and biophysical investigation of its stability and DNA binding ability. Transcriptional analysis revealed the upregulation of BldR2 expression by aromatic compounds in the latelogarithmic growth phase and allowed the identification of cisacting sequences. Our results suggest that BldR2 possesses in solution a dimeric structure and a high stability against both temperature and chemical denaturing agents; the protein binds site specifically to its own promoter, Sso1082, with a micromolar binding affinity at two palindromic sites overlapping TATA-BRE and the transcription start site. Benzaldehyde and salicylate, ligands of MarR members, are antagonists of binding of DNA by BldR2. Moreover, two single-point mutants of BldR2, R19A and A65S, properly designed for obtaining information about the dimerization and the DNA binding sites of the protein, have been produced and characterized. The results point out an involvement of BldR2 in the regulation of the stress response to aromatic compounds and point to arginine 19 as a key amino acid involved in protein dimerization, while the introduction of serine 65 increases the DNA affinity of the protein, making it comparable with those of other members of the MarR family.