Molecular bases of sensor/operator selectivity in MerR monovalent metal ion sensors.

HUMBERT MV; CHECA SK; SONCINI FC

Salta

Congreso; 3rd Latin American Protein Society Meeting. XXXIX Annual Meeting of the Argentinean Biophysical Society (SAB 2010).; 2010

Resistance to overload of the essential copper ion or the presence of toxic silver and gold ions in Salmonella is coordinated by two paralogous transcription factors of the MerR family, CueR and GolS. Although highly similar, these regulators diverged in signal recognition, as GolS prefers Au(I) ions while CueR promotes similar levels of transcription in response to either Cu(I), Ag(I) or Au(I) and control two different set of genes. We previously found that in spite of sharing similarity at their target binding sites, each factor displays in vitro higher affinity for their innate operators than for the binding sites of the non-cognate regulator. This is achieved by the presence of conserved operator´s bases that distinguish GolS from CueR regulated genes. Here, by using fragment swapping and site directed mutagenesis plus reporter-gene expression assays, as well as in silico modeling, we identified the protein’s regions within the N-terminal DNA binding domain responsible for the selective recognition of their innate operators. We uncover that a single residue at position 16 of the a2-helix, which is an invariant M in all GolS xenologues while in CueR-like proteins varies between a T, an A, or an S, is essential for binding to the cognate target binding sites in vivo. These results highlight the molecular bases of regulator/operator selectivity among paralogous MerR regulators and the co-evolution of transcriptional regulator target binding sites to properly respond against metal injury.