3.E.1.1.6
Sensory rhodopsin (green-light-activated photoreceptor; does not transport ions) (Jung et al., 2003). Has all-trans-retinal when dark adapted, but 11-cis-retinal when light adapted due to reversible interconversion (Sineshchekov et al., 2005).  Anabaena sensory rhodopsin, a photochromic sensor that interacts with a soluble 14-kDa cytoplasmic transducer that is encoded on the same operon, interconverts between all-trans-15-anti and 13-cis-15-syn retinal forms depending on the wavelength of illumination, although only the former participates in a photocycle with a signaling M intermediate (Dong et al. 2016). A mutation in the cytoplasmic half-channel of the protein, replacing Asp217 with Glu (D217E), results in the creation of a light-driven, single- photon, inward proton transporter. Dong et al. 2016 presented the 2.3 A structure of dark-adapted D217E ASR, which reveals changes in the water network surrounding Glu217, as well as a shift in the carbon backbone near retinal-binding Lys210, illustrating a possible pathway leading to the protonation of Glu217 in the cytoplasmic half-channel, located 15 A from the Schiff base.