LAUSR

In order to respond to external stimuli, bacteria have evolved sensor proteins linking external signals to intracellular outputs that can then regulate downstream pathways and phenotypes. Globin coupled sensor proteins (GCSs) serve to link environmental O2 levels to cellular processes by coupling a heme-containing sensor globin domain to a catalytic output domain. However, the mechanism by which O2 binding activates these proteins is currently unknown. To provide insights into the signaling mechanism, two distinct dimeric complexes of the isolated globin domain of the GCS from Bordetella pertussis (BpeGlobin) were solved via X-ray crystallography in which differences in ligand-bound states were observed. Both monomers of one dimer contain Fe(II)–O2 states, while the other dimer consists of the Fe(III)–H2O and Fe(II)–O2 states. These data provide the first molecular insights into the heme pocket conformation of the active Fe(II)–O2 form of these enzymes. In addition, heme distortion modes and heme–protein ...