Characterization of a CueR variant that responds to +1 and +2 heavy metal ions

LESCANO, J.; SONCINI, F. C.; CHECA, S. K.

Paraná

Congreso; LIV Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2018

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Resistance to toxic heavy metals in bacteria is controlled by cytoplasmic metalloregulators of the MerR family. These transcriptional activators bind metals ions with high affinity at the dimer interface, using residues from both monomers. According to the array of available ligands at the metal-coordination environment, MerR sensors are group in three categories: the CueR-like Cu(I)/Ag(I)/Au(I) sensors, the archetypal MerR Hg(II) sensors and the ZntR-like Zn(II)/Pb(II)/Cd(II) sensors. CueR coordinates +1 ions using two conserved cysteine residues (C112 and C120) from one monomer. MerR and ZntR-like sensors use, in addition, a third C residue from the other monomer to bind +2 ions that require a high number of coordination ligands. Interestingly, CueR and its orthologues have a conserved serine (S77) in place of the third cysteine, but its relevance is still unknown. We previously shown that a Salmonella Typhimurium strain carrying a cueR-S77C mutant allele activates CueR controlled genes in response to Cu(I), Ag(I), Au(I), and also to Hg(II). Furthermore, this mutant sensor also responds to Pb(II), Cd(II) and Co(II) in a strain lacking the Zn(II)/Pb(II)/Cd(II) transporter ZntA. Here, we reproduced the S77C mutation in the EscherichiacoliCueRortholog from which structural data is available. Using specific reporter genes, we validated the response of ECCueR-S77C to +1 and +2 metal ions. We also analyzed and compared the interaction of ECCueR-S77C and ECCueR with Pb(II) or Co(II) by recording the UV−vis spectra. Our results contribute to understand the importance of S77 in CueR-like proteins for the exclusion of +2 ions from the metal binding site.