MOLECULAR BASES OF METAL/OPERATOR SELECTIVITY IN MerR MONOVALENT METAL ION SENSORS

IBÁÑEZ MM; HUMBERT MV; ZAFRA M; CERMINATI S; CHECA SK; SONCINI FC

Hotel Catalinas Park, Tucumán, Argentina

Congreso; XLV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2009

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Metal ions are essential in biology and play key roles in the structure-function of a large number of proteins. They can also be toxic, especially at high concentrations. Intracellular metal ion concentrations must therefore be tightly controlled to maintain normal metabolism. In Salmonella, two related transcriptional regulators, CueR and GolS, ensure resistance against Cu and Au ions. CueR is essential to maintain copper homeostasis, while GolS is dedicated to protect the cell from the toxic effects of gold. We have identified amino acid residues at the GolS metal-binding loop that direct Au(I) recognition. In addition, we determined the operator sequences recognized by these regulators, and established the nucleotide bases responsible for the regulator-operator selectivity among GolS and CueR regulated promoters. Here, by using in silico modeling, site- and loop-directed mutagenesis, as well as reporter expression assays, we identify the regions in both transcriptional regulators responsible for the recognition/selection of their innate operators. In addition, we establish the role of specific amino acids residues that govern both, monovalent metal ion sensing and divalent metal ions exclusion from the metal binding loop. Our results highlight the mechanisms employed by these regulators to modulate the expression of their target genes without affecting global metal homeostasis.