3.E.1.1.16
Microbial (bacterial) rhodopsin, Bop2, of 246 aas and 7 TMSs.  It has no proton-pumping activity but is potentially capable of functioning as a sensory SRII-like protein. The chromophore contains 36.5% all-trans-, 7.6% 11-cis- and 56.4% 13-cis-retinal in the dark and 30.1% 11-cis- and 47.7% 13-cis-retinal upon illumination with >460 nm light (Sudo et al. 2011).  Haloquadratum walsbyi (Hw) survives at high MgCl₂ concentrations, with a total of three MRhos identified, including (1) a high-acid-tolerance light-driven proton outward pump, HwBR, (2) a chloride-insensitive chloride pump, HwHR, and (3) HwMR, the sole magnesium-sensitive MRho among all tested MRho proteins from Haloarchaea. D84 is one of the key residues mediating such magnesium ion association in HwMR. Sequence analysis and molecular modeling suggested HwMR to have an extra H8 helix in the cytosolic region like those in signal-transduction-type MRho of deltarhodopsin-3 (dR-3) and Anabaena sensory rhodopsin (ASR) (Ko et al. 2022).