Protein signatures that confer proper metal recognition and signal transduction in MerR metalloregulators

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

Ciudad Autónoma de Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias, LIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2017

Sociedades de Biociencias

Transcriptional regulation is the main cellular mechanism bacteria employ to control homeostasis or resistance to essential and harmful metal ions. Our group focused on metallo-regulators of the MerR family, dimeric and bifunctional 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 Cu(I) or Ag(I), or divalent ions. We found that two residues from the metal binding loop 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 composing the metal binding loop of GolS determine proper recognition of metal ions and transcriptional activation. First, we performed swapping of the metal binding loop 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. Then, we 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 suggested 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 to allow activation of transcription