The metal selectivity of GolS is achieved by specific amino acids in the C-terminal binding loop

IBÁÑEZ, MARÍA MARTA; CHECA, SUSANA K; SONCINI, FERNANDO C

Villa Carlos Paz, Córdoba, Argentina

Congreso; Argentine Society for Biochemistry and Molecular Biology research. XLII Reunion Meeting. 44th Annual Meeting.; 2008

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

Salmonella depends on two MerR regulators to monitor the environmental concentration of monovalent metal ions: the copper-regulator CueR which governs copper homeostasis, and the Salmonella-specific GolS, responsible for gold resistance. CueR is able to detect Au or Cu ions with similar affinities. On the other hand, GolS is 52 times more responsive to Au than to Cu, and this metal-discrimination relies on the C-terminal CX7C loop of the sensor protein. Replacement of the C residues of the metal-binding loop or of a conserved S residue within the dimerization domain abrogated metal-dependent activity of the regulator, indicating that these residues are essential for the regulator’s function. To dissect the role of the individual amino acid residues within the metal-binding region of GolS in metal-selectivity, a series of mutant proteins were constructed, in which each residue was replaced by the one present in CueR-like regulators. The replacement of an A residue in the position 113 of GolS for a P rendered a mutant regulator with similar affinities to Au(I) or Cu(I). Our results suggest that metal-discrimination in GolS relies on the spatial conformation that the metal-binding loop adopts rather than on the presence of particular residues within it, favouring the interaction of Au(I) with a larger ionic radius, and hindering the interaction of Cu(I) with a smaller ionic size.