Retinal conformation

Okada T, Sugihara M, Bondar AN, Elstner M, Entel P, Buss V (2004) The retinal conformation and its environment in rhodopsin in light of a new 2.2 angstrom crystal structure. J. Mol. Biol. 342(2) 571-583... 

Brown ME, Martinez-Mayorga K, Nakanishi K et al (2009) Retinal conformation and dynamics in activation of rhodopsin illuminated by solid-state H-2 NMR spectroscopy. Photochem Photobiol 85 442-453... 

G. Bringmann, T. A. M. Gulder, M. Reichert and T. Gulder, The Online Assignment of the Absolute Configuration of Natural Products UPLC-CD in Combination with Quantum Chemical CD Calculations , Chirality, 2008,20,628. M. F. Brown, K. Martinez-Mayorga, K. Nakanishi, G. F. J. Salgado and A. V. Struts, Retinal Conformation and Dynamics in Activation of Rhod-opsin Illuminated by Solid-State NMR Spectroscopy , Photochem. Pho-tobiol., 2009, 85, 442. 

Visualpigmentsandbacteriorhodopsin. Retinal conformation in the photocycle intermediates state of protonation of the retinal-protein Schiff base... 

Figure 12.4 The light-absorbing pigment retinal undergoes a conformational change called isomerization, when it absorbs light.

Fi re 12.6 Schematic diagram Illustrating the proton movements in the photocycle of bacteriorhodopsin. The protein adopts two main conformational states, tense (T) and relaxed (R). The T state binds trans-tetinal tightly and the R state binds c/s-retinal. (a) Stmcture of bacteriorhodopsin in the T state with hflus-retinal bound to Lys 216 via a Schiff base, (b) A proton is transferred from the Schiff base to Asp 85 following isomerization of retinal and a conformational change of the protein. 

The CP MAS NMR spectroscopy has been also extensively used for studies of proteins containing retinylidene chromophore like proteorhodopsin or bacteriorhodopsin. Bacteriorhodopsin is a protein component of purple membrane of Halobacterium salinarium.71 7 This protein contains 248 amino acids residues, forming a 7-helix bundle and a retinal chromophore covalently bound to Lys-216 via a Schiff base linkage. It is a light-driven proton pump that translocates protons from the inside to the outside of the cell. After photoisomerization of retinal, the reaction cycle is described by several intermediate states (J, K, L, M, N, O). Between L and M intermediate states, a proton transfer takes place from the protonated Schiff base to the anionic Asp85 at the central part of the protein. In the M and/or N intermediate states, the global conformational changes of the protein backbone take place. 

The active compound within the bacillary layer is retinal. To simplify the photo-physics within the rods and cones hugely, absorption of a photon initiates a series of conformational changes that lead ultimately to photo-isomerization of retinal from the 11-cis isomer to the 11-trans isomer see Figure 9.20. The uncoiling of the molecule following photo-excitation triggers a neural impulse, which is detected and deconvoluted by the brain. The photochemical reaction is breakage and, after rotation, re-formation of the C=C bond. 

FIGURE 45. Orientation and conformation of retinal in bR, constructed from the individual methyl group orientations that have been determined by solid-state 2H NMR. The angles 6 of the C—CD3 bond vectors with respect to the membrane normal (N) were evaluated for Cis (37°), C49 (40°) and C20 (32°) from the zero-tilt spectra shown in Figure 44 and with the aid of line-shape simulation of the tilt series in Figure 42 and 43. Reprinted with permission from Reference 57. Copyright (1994) American Chemical Society... 

FIGURE 47. Three-dimensional structure of the cyclohexene ring of retinal in bR as determined by 2H NMR, relative to the membrane surface in the x-y plane. Analysis of the orientations of the three deuterium labeled methyl groups on the puckered ring (skew around C1-C6) indicates that the chromophore has a 6s-trans conformation around the C6-C7 bond. Reprinted with permission from Reference 60. Copyright (1997) American Chemical Society... 

The absorption of light by CM-retinal converts it to the trans-form which induces a conformational change in opsin. One photon catalyses the isomerisation of one molecule of... 

In such a way we were able to conclude that the illumination of suspensions of photoreceptor outer segments by 450 nm light at 77°K, which was known to result in the rhodopsin— prelumirhodopsin transition (corresponding to 11-cis-retinal— transretinal photoisomerization of chromophore), leads also to the appearance of some reduction centers and to the conformational change of membrane. 

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