The Heme-Based Oxygen Sensor Rhizobium etli FixL: Influence of Auxiliary Ligands on Heme Redox Potential and Implications on the Enzyme Activity.

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.