Globin domain interactions control heme pocket conformation and oligomerization of globin coupled sensors

Globin coupled sensors (GCS) are O₂-sensing proteins used by bacteria to monitor the surrounding gaseous environment. To investigate the biphasic O₂ dissociation kinetics observed for full-length GCS proteins, isolated globin domains from Pectobacterium carotovorum ssp. carotovorum (PccGlobin), and Bordetella pertussis (BpeGlobin), have been characterized. PccGlobin is found to be dimeric, while BpeGlobin is monomeric, indicating key differences in the globin domain dimer interface. Through characterization of wild type globin domains and globin variants with mutations at the dimer interface and within the distal pocket, dimerization of the globin domain is demonstrated to correlate with biphasic dissociation kinetics. Furthermore, a distal pocket tyrosine is identified as the primary hydrogen bond donor, while a secondary hydrogen bond donor within the distal heme pocket is involved in conformation(s) that lead to the second O₂ dissociation rate. These findings highlight the role of the globin dimer interface in controlling properties of both the heme pocket and full-length GCS proteins.