Honorio-Felício Nathalie, Carepo Marta S P, de F Paulo Tércio, de França Lopes Luiz Gonzaga, Sousa Eduardo H S, Diógenes Izaura C N, Bernhardt Paul V
Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760, Fortaleza, Ceará, Brazil; School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, 4072, Australia.
Laboratório de Bioinorgânica, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, CEP 60455-760, Fortaleza, Ceará, Brazil.
J Inorg Biochem. 2016 Nov;164:34-41. doi: 10.1016/j.jinorgbio.2016.08.009. Epub 2016 Aug 26.
Conformational changes associated to sensing mechanisms of heme-based protein sensors are a key molecular event that seems to modulate not only the protein activity but also the potential of the Fe redox couple of the heme domain. In this work, midpoint potentials (E) assigned to the Fe redox couple of the heme domain of FixL from Rhizobium etli (ReFixL) in the unliganded and liganded states were determined by spectroelectrochemistry in the presence of inorganic mediators. In comparison to the unliganded ReFixL protein (+19mV), the binding to ligands that switch off the kinase activity induces a negative shift, i. e. E=-51, -57 and -156mV for O, imidazole and CN, respectively. Upon binding to CO, which does not affect the kinase active, E was observed at +21mV. The potential values observed for Fe of the heme domain of ReFixL upon binding to CO and O do not follow the expected trend based on thermodynamics, assuming that positive potential shift would be expected for ligands that bind to and therefore stabilize the Fe state. Our results suggest that the conformational changes that switch off kinase activity upon O binding have knock-on effects to the local environment of the heme, such as solvent rearrangement, destabilize the Fe state and counterbalances the Fe-stabilizing influence of the O ligand.
