Structural and functional characterization of the globin-coupled sensors of Azotobacter vinelandii and Bordetella pertussis

Aims: Structural and functional characterization of the globin coupled sensors (GCS) of Azotobacter vinelandii (AvGReg) and Bordetella pertussis (BpeGReg). Results: UV/Vis and RR spectroscopies confirm the presence in AvGReg and BpeGReg of a globin domain capable of reversible gaseous ligand binding. In AvGReg an influence of the transmitter domain on the heme proximal region of the globin domain can be seen, and k'CO is higher than for other GCSs. The O2 binding kinetics suggest the presence of an open and a closed conformation. As for BpeGReg, the fully oxygenated AvGReg show a very high DGC activity. The CO rebinding to BpeGReg indicates that intra- and intermolecular interactions influence the ligand binding. The globin domains of both proteins (AvGReg-Gb and BpeGreg-Gb*) share the same GCS fold, a similar proximal but a different distal side structure. They homodimerize through a G-H helical bundle as in other GCS. However, BpeGReg-Gb* shows also a second dimerization mode. Innovation: This paper extends our knowledge on the GCS proteins and contributes to a better understanding of the GCSs' role in the formation of bacterial biofilms. Conclusions: AvGReg and BpeGreg conform to the GCS family, share a similar overall structure but they have different properties in terms of the ligand binding. In particular, AvGreg shows an open and closed conformation that in the latter form will very tightly bind oxygen. BpeGReg has only one closed conformation. In both proteins, it is the fully oxygenated GCS form that catalyzes the production of the second messenger.