The heme pocket of the globin domain of the globin-coupled sensor of Geobacter sulfurreducens--an EPR study.

The globin-coupled sensor (GCS) of Geobacter sulfurreducens is unique amongst GCSs in that its signalling domain is a transmembrane domain with yet unknown function. In the present work we use X-band continuous-wave and pulsed electron paramagnetic resonance (EPR) to investigate the ferric form of the globin domain of the G. sulfurreducens GCS (GsGCS(162)) at pH 8.5. This form shows a unique bis-histidine coordination of the heme with the F8His and E11His. In contrast with previous crystal structure data, where three conformers of the heme structure were identified, ferric GsGCS(162) assumes only one conformation in frozen solution. The EPR data of ferric GsGCS162 are compared in detail with those of other bis-histidine coordinated globins, including other GCS systems.