Dissecting metal-recognition selectivity by MerR monovalent metal ion sensors

IBÁÑEZ MM; CHECA SK; SONCINI FC

Salta

Congreso; 3rd Latin American Protein Society Meeting; 2010

Latin American Protein Society

Metal ions are important at trace amounts in biology for the structure and function of a large number of proteins, but they are also toxic even at low concentrations. Bacteria have evolved a wide variety of mechanisms to deal with these essential and at the same time toxic nutrients. In Salmonella, two transcriptional regulators of the MerR family are responsible for the detection and response to copper and gold ions, respectively. While the ancestral regulator CueR is able to detect Au or Cu ions with similar affinities, the Salmonella-specific regulator GolS is 52 times more responsive to Au(I) than to Cu(I). We have previously demonstrated that the difference in metal-discrimination relies on the C-terminal CX7C loop of these sensor proteins. Here we analyze the role of the amino acid residues of the metal binding loop and the alpha-helix dimerization domain of these proteins on metal discrimination. We find that the metal binding loop residue at position 113 of GolS is essential for the preferential recognition of Au(I). Moreover, the identity of amino acid residue at this position is conserved among GolS-xenologs and differs from those present in CueR-like regulators. We also establish that the residue at position 77 of the dimerization helix in monovalent metal sensors of the MerR family effectively excluded divalent metal ions from the metal binding loop. Our results highlight the molecular bases that allow these regulators to coordinate the appropriate metal at the dimer interface in order to properly direct the response to metal injury.