3.E.1.6.3
Gloeobacter rhodopsin (GT) of 298 aas and 7 TMSs (associates with salinixanthin, the light-harvesting carotenoid antenna of xanthorhodopsin) (Imasheva et al., 2009; Hashimoto et al., 2010).  Expression in a chemotrophic E. coli enabled light-driven phototrophic energy generation (Kim et al. 2017). The X-ray crystallographic structure and oligomeric state have been described (Morizumi et al. 2019). The structural characteristics of GR's hydrogen bonding network in the transmembrane domain as well as the displacement of extracellular sides of the TMS resemble those of XR. The pH-dependent pentamer form of GR was documented. Structural motifs (extended helices, 3-omega motif and flipped B-C loop) typical of other characterized rhodopsins, were also identified (Morizumi et al. 2019).  This proton outward pumping rhodopsin interacts with a helix-turn-helix transcriptional regulator and regulats gene expression. ATP-binding cassette (ABC) transporters and the self-regulation of G. violaceus transcriptional regulator (GvTcR) are regulated by light, and gene regulation was observed in G. violaceus using the real-time PCR (Shim et al. 2024).