PROTEIN SIGNATURES THAT ALLOW PROPER METAL RECOGNITION AND SIGNAL TRANSDUCTION IN MerR METALLOREGULATORS

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

Cuidad Autónoma de Buenos Aires

Congreso; Reunión conjunta de Sociedades de Biociencias; 2017

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

Transcriptional regulation is the main cellular mechanism bacteria employ to control homeostasis/resistance to essential and harmful metal ions. Our group focuses on metalloregulators of the MerR family, dimeric proteins that detect the ions in the cytoplasm and activate transcription of specific transporters or detoxification enzymes to eliminate the intoxicant. Among them, two groups with similar structure can be clearly distinguished depending on the charge (+1 or +2) of the metal ion they sense. Previously, we discerned the molecular bases that allow GolS, a Salmonella specific sensor, to discriminate Au(I) from other metal ions including Cu(I) or Ag(I), or divalent ions. We found that two residues from the metal binding loop (MBL) between the two coordinating cysteines (A113 and P118) are crucial for Au discrimination, while a single serine residue (S77) that is located near the metal coordination environment is essential from excluding +2 charge metals from the binding site. Here, we analyzed how the size and identity of the residues of the MBL determine proper recognition of metal ions and transcriptional activation. We swapped the MBL of GolS or CueR (the paralogous non-selective monovalent metal ions sensor) for the same region of ZntR or MerR, two representatives of the divalent metal ion sensor group, and analyzed the response of the new variants to different monovalent (Au and Cu) or divalent (Hg, Cd, Pb and Zn) metal ions by measuring transcriptional activation of specific reporter genes. Our results suggest that besides the presence and proper location of essential ligands, the size of the metal binding loop is the main determinant of proper metal recognition and signal transduction that allow activation of transcription of target genes.