Sensory rhodopsins

Sineshchekov, O. A., V. D. Trivedi et al. (2005). Photochromicity of Anabaena sensory rhodopsin, an atypical microbial receptor with a cw-retinal light-adapted form. J. Biol. Chem. 280(15) 14663-14668. 

Vogeley, L., O. A. Sineshchekov et al. (2004). Anabaena sensory rhodopsin A photochromic color sensor at 2.0 angstrom. Science 306(5700) 1390-1393. 

Sensory rhodopsin (sR) and proteorhodopsin 4.12.1. Sensory rhodopsin Halobacteria contain a family of four retinal proteins, bR, halorhodopsin (hR), sensory rhodopsin I (sR I), and phobor-hodopsin (pR or sensory rhodopsin II, sR II), which carry two distinct functions through common photochemical reactions. In particular, bR... 

Archaebacterial rhodopsins may provide models for signal transduction and ion transport.62 Spin labels were attached to sensory rhodopsin (pSRII) and its transducer (pHTrll) from Natronobacterium pharaonis. Interspin distance determined by line-shape analysis including a Gaussian distribution of distances revealed a 2 2 complex with 2-fold symmetry. Distances for 26 pairs of spin labels defined the orientation of the TM helices of pHtrll relative to the F and G helices of pSRII.63 Light excitation causes a flap-like movement of helix F of NpSRII that induces a rotary motion of a helix in the transmembrane domain of the transducer.62... 

Sensory rhodopsin II (SRII, also called phobo-rhodopsin) is specialized for repellant phototaxis.5913 Blue light converts SRII487 in < 1 ms to UV-absorbing SRII360. It decays in 100 ms to SRn5/W) which reverts to the initial SRII487 in 0.5 s. The cycle is accompanied by swimming reversals that result in a repellent... 

Klare, J. P., Gordeliy, V. I., Labahn, J., Biildt, G., Steinhoff, H.-J., and Engelhard, M. (2004). The archaeal sensory rhodopsin II/transducer complex A model for transmembrane signal transfer. FEBS Lett. 564, 219—224. 

Marwan, W. and Oesterhelt, D., Quantitation of photochromism of sensory rhodopsin-I by computerized tracking of Halobacterium halobium cells, J. Mol. Biol., 215, 211, 1990. 

Sensory rhodopsin (SRII20 and SRII/Htrll93) Proteoliposome pellets 0.7 ppm 228-278 K Reconstituted with native lipids... 

Luecke, H., Schobert, B., Lanyi,J. K., Spudich, E. N., and SpudichJ. L. (2001). Crystal structure of sensory rhodopsin II at 2.4 angstroms insights into color tuning and transducer interaction. Science 293, 1499-1503. 

Both in the case of sensory rhodopsin in humans and of bacteriorhodopsin (a heptahelical membrane protein in halobacteria which is not coupled to a G protein) translocation of a Schiff-base proton is the essential step in making the protein functional (reviewed in ref 58). In rhodopsin the conversion of the inactive AH state to the AHI state that binds to the G protein is coupled to proton transfer from the Schiff base to the counterion, Glul 13, and proton uptake from the medium to the highly conserved Glul34, which serves as proton acceptor. Based on that similarity, one could consider sensory rhodopsin as an incomplete proton pump. Furthermore, a property shared by all G-protein-coupled receptors is a triplet, formed by residues 134-136 in rhodopsin, consisting of Glu-Arg-Tyr. The consequences of mutational replacement of Glul34 supports the notion that the state of protonation of this amino add is crudal for activity, and that its protonation triggers the conformational transition of the receptor from the inactive to the active state. 

However, subsequent studies on halobacterial retinal proteins seemed to argue against the photoreceptor function of bacteriorhodopsin. It was found that (i) bacteriorhodopsin operates as a light-driven H pump and (ii) in the same halobacteria there are two other retinal proteins, i.e., sensory rhodopsin I and sensory rhodopsin II (also known as photorhodopsin) which are specialized in photoreception rather than in H pumping, being present in much smaller amounts than bacteriorhodopsin [36-43]. It was shown that... 

The above reasoning was recently confirmed by several pieces of indirect evidence. It was found that in H. halobium (i) protonophorous uncouplers decrease A/in and cause a repellent effect [45], (ii) cyanide and DCCD have no effect on the photoresponse of a mutant which possesses sensory rhodopsins but no bacteriorhodopsin [48], and (iii) in a similar mutant, A l is not involved in photosensing [49]. 

By using an enzymatic assay for fumarate which detects the compound in the lower pmol range the kinetics of fumarate release after activation of sensory rhodopsin-II could be measured. The concentration of fumarate released from the protein-bound pool increased transiently after a blue light pulse. The kinetics correlate consistently... 

It is an important experimental advantage that the halobacterial photoreceptor apoproteins (so-called sensory opsins, SO) are expressed by the cell even in absence of retinal. Retinal biosynthesis can be blocked either genetically or simply by addition of nicotine to a growing culture. Upon addition of external retinal, active photoreceptors spontaneously reconstitute in vivo. This kind of experiment showed that photoreception is strictly retinal-dependent. By incorporation of artificially synthesized retinal analogues into sensory opsins, John Spudich and coworkers obtained valuable information on the activation process of the sensory rhodopsins. 

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