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Protoglobins (Pgbs) Pgbs are single-domain globins of yet unknown biological function. Included in this subfamily are Pgbs from the strictly anaerobic methanogen Methanosarcina acetivorans (MaPgb) and from the obligate aerobic hyperthermophile Aeropyrum pernix (ApPgb). MaPgb is a dimeric globin which in addition to the 3-on-3 helical sandwich contains an N-terminal extension. This extension, along with other Pgb-specific loops buries the heme within the protein; two orthogonal apolar tunnels grant access of small ligand molecules to the heme. Like other globins, MaPgb can bind O2, CO and NO reversibly in vitro, however it has as unusually low O2 dissociation rate, along with a large structural distortion of the heme moiety. CO binding to and dissociation from the heme occurs through biphasic kinetics. ApPgb also contains heme, and can bind O2, CO and NO. This subfamily belongs to a family which includes the globin-coupled-sensors (GCSs) and single-domain sensor globins. It has been demonstrated that Pgbs and other single-domain globins can function as sensors, when coupled to an appropriate regulator domain. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",