THE METAL-BINDING LOOP DETERMINES METAL SELECTIVITY IN CUER-LIKE TRANSCRIPTIONAL REGULATORS

IBAÑEZ, MARIA MARTA; CHECA, SUSANA K.; SONCINI, F. C.

Mar del Plata

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2007

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Metal-dependent transcriptional regulatory systems are the major cellular mechanism that bacteria employ to control metal homeostasis or resistance to harmful non-essential transition elements. Salmonella has two transcriptional regulators of the MerR family that respond to monovalent metal ions: CueR, which is involved in copper homeostasis, and GolS, which is responsible for gold detoxification. Both proteins share 42 % amino acid sequence identity but, unlike CueR, GolS can discriminate between Au and Cu ions. To understand how GolS discriminates between these two related metal ions we first performed a comparison of the protein regions that can influence metal binding: the metal-binding loop (between C112 and C120), the C-terminal region after the loop, and the amino acid residues surrounding S77 in the dimerization domain. These regions were modified in GolS by loop- or site-directed mutagenesis to resemble these of CueR, and introduced into the chromosome, replacing the wild-type copy of golS. The response of each mutant regulator to either Au or Cu ions was analyzed by monitoring expression of GolS-controlled genes. Our results indicate that the amino acid residues surronding the two conserved Cys at the metal binding loop are essential for the discrimination between the two metal ions. These findings can be used for the construction of Group IB metal-specific biosensors.