Globin sensor domain of globin-coupled-sensors (GCSs), protoglobins (Pgbs), and sensor single-domain globins (SSDgbs); S family
This family includes sensor domains which binds porphyrins, and other non-heme cofactors. GCSs have an N-terminal sensor domain coupled to a functional domain. For heme-bound oxygen sensing/binding globin domains, O2 binds to/dissociates from the heme iron complex inducing a structural change in the sensor domain, which is then transduced to the functional domain, switching on (or off) the function of the latter. Functional domains include DGC/GGDEF, EAL, histidine kinase, MCP, PAS, and GAF domains. Characterized members include Bacillus subtilis heme-based aerotaxis transducer (HemAT-Bs) which has a sensor domain coupled to an MCP domain. HemAT-Bs mediates an aerophilic response, and may control the movement direction of bacteria and archaea. Its MCP domain interacts with the CheA histidine kinase, a component of the CheA/CheY signal transduction system that regulates the rotational direction of flagellar motors. Another GCS having the sensor domain coupled to an MCP domain is Caulobacter crescentus McpB. McpB is encoded by a gene which lies adjacent to the major chemotaxis operon. Like McpA (encoded on this operon), McpB has three potential methylation sites, a C-terminal CheBR docking motif, and a motif needed for proteolysis via a ClpX-dependent pathway during the swarmer-to-stalked cell transition. Also included is Geobacter sulfurreducens GCS, a GCS of unknown function, in which the sensor domain is coupled to a transmembrane signal-transduction domain. Pgbs are single-domain globins of unknown function. Methanosarcina acetivorans Pgbs is dimeric and has an N-terminal extension, which together with other Pgb-specific loops, buries the heme within the protein; small ligand molecules gain access to the heme via two orthogonal apolar tunnels. 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.",