Retinal, in rhodopsin

Migani A, Sinicropi A, Ferr N, Cembran A, Garavelli M, Olivucci M (2004) Structure of the intersection space associated with Z/E photoisomerization of retinal in rhodopsin proteins. Faraday discuss 127 179... 

The molecular event that triggers the visual process is the light-induced transformation of the 11-c form of retinal in rhodopsin to the aJi-trans form. 

In a crystal structure47111-ds-retinal has the 12-s-cis conformation shown at the top in Eq. 23-36 rather than the 12-s-frans conformation at the center and in which there is severe steric hindrance between the 10-H and 13-CH3. Nevertheless, H-and 13C-NMR spectroscopy suggest that the retinal in rhodopsin is in a twisted 12-s-frans conformation.472 4723 The Schiff base of 11-ds-retinal with N-butylamine has an absorption maximum at -360 nm but N-protonation, as in the structure in Eq. 23-36, shifts the maximum to 440 nm with emax = 40,600 M 1 cm 1 (Fig. 23-42). This large shift in the wavelength of the absorption maximum (the opsin shift) indicates that binding to opsin stabiliz-... 

The primary photochemical process of vision is therefore the cis-trans isomerization of retinal in rhodopsin. The free protein opsin then leads to the production of the nerve impulse through a secondary biochemical process... 

In a model proposed by Lewis [228] the effect of the excited state of retinal on the conformational state of the protein is considered to be the first step of the excitation mechanism. Charge redistribution in the retinal by excitation with light would have the consequence of vibrationally exciting and perturbing the ground state conformation of the protein, i.e., excited retinal would induce transient charge density assisted bond rearrangements (e.g., proton translocation). Subsequently, retinal would assume such an isomeric and conformational state so as to stabilize maximally the new protein structure established. In this model, 11-m to trans isomerization would not be involved in the primary process, but would serve to provide irreversibility for efficient quantum detection. It was also proposed that either the 9-m-retinal (in isorhodopsin) or the 11-m-retinal (in rhodopsin) could yield the same, common... 

A series of hydroretinals were synthesized and were bound to bovine opsin to form visual pigment analogs, the hydrorhodopsins [92]. Model protonated Schiff bases were also prepared from each of these retinals, and the magnitudes of the opsin shifts were determined. Table 1 summarizes the data obtained and shows the opsin shift for bovine rhodopsin for comparative purposes. Binding studies were also carried out to ascertain that the hydroretinals occupy the same binding site as 11-cK-retinal in rhodopsin. This is required to show the relevance of the data to the natural system. 

H and IS-CHg. Nevertheless, H-and C-NMR spectroscopy suggest that the retinal in rhodopsin is... 

In a crystal structure 11-ds-retinal has the 12-s-cis conformation shown at the top in Eq. 23-36 rather than the 12-s-trans conformation at the center and in which there is severe steric hindrance between the 10-H and I3-CH3. Nevertheless, H-and C-NMR spectroscopy suggest that the retinal in rhodopsin is... 

Figure 5.2.6 Hypothetical concerted cis-trans isomerizations and conformational changes of retinal in rhodopsin. The final rmni-retinal would also have high conformational strain, because the methyl group on C9 interacts with the proton on C12.

The ds-trans isomerization of retinal in rhodopsin triggers the transmission of an impulse to the optic nerve and is the primary photochemical event in vision. 

C13-C14-C15 regions (Fig. 6). The large change at C13, C9, and C17 may be attributed to the break of the dull3 salt bridge, van der Waals contact, and local hydrophobic environmental changes due to the displacements of the helices upon activation. In addition to the studies on the retinal in rhodopsin, the structure of... 

Yamada, A., T. Kakitani, et al. (2002). A computational study on the stability of the protonated Schiff base of retinal in rhodopsin. Chemical Physics Letters 366(5-6) 670-675. 

As other double bonded chromophores, the imine chromophore is liable to photochemical E/Z isomerization. The problem has been examined in detail for N-benzylidene aniline and derivatives for both the experimental and computational (TD DFT) point of view. This has given a detailed picture of the effect of substituents on the various steps involved and thus has allowed to predict the best choice of molecules that work as optimal switches , that is are characterized by a well apparent photochromic effect, while maintaining a reasonable thermal stability.High level ab initio calculations have been devoted to the analysis of the isomerization of tZt-penta-3,5-dieniminium cation, a simplified model for the protonated Schiff base of W-cis retinal in rhodopsin. ... 

As an apphcation of this approach, it has recently been suggested to use a vibronicaUy coupled two-mode two-state system to model the photoisomerization of retinal in rhodopsin. Due to its importance for the first step in vision, there has been considerable effort to understand this photoreaction. The matrix elements of the molecular Hamiltonian... 

Abe M, Ohtsuld Y, Fujimura Y, Domcke W (2005) Optimal control of ultrafast cis-trans photisomerisation of retinal in rhodopsin via a conical intersection. J Chem Phys 123 144508... 

In the dark retinal in rhodopsin is in the 11-cfs-configuration. Irradiation of rhodopsin leads to a series of conformational changes which can be noted by the disappearance and appearance of various intermediates of different colours. 

Rhodopsin which is a brown [Red] coloured chromoprotein found in rods and synthesized from vitamin A, get bleached in presence of light and resynthesized in dark. The first step is the conversion of Rhodopsin into Bathorhodopsin after the absorption of light. This conversion needs only tens of picoseconds and each subsequent step is 10 -10 times slower than its previous step. Current opinion ascribes the changes to the inability of the straight all-trans-retinal to be sterically accommodated on the surface of the opsin, only bent 11-ds-retinal fitting into the protein. In the dark, the retinal in rhodopsin is in the 11-cis conformation. Absorption of photon leads to photoisomerisation of the double bond of the 11-ds-retinal in rhodopsin. This alters the configuration of the opsin and opsin changes activities of the associated hetero trimeric G protein, which is called transducin or Gt 1. Photoisomerisation leads to the formation of... 

Vision involves cis-trans photoisomerization of a chromophore and many studies have been done using different models/ For example, a CASSCF/AMBER procedure has been used to study the nonadiabatic dynamics of retinal in rhodopsin proteins/ In another study, a simple model of a photosynthetic center was examined by Worth and Cederbaum. They proposed that the presence of conical intersections facilitated the long-range intermolecular photo-initiated electron transfer between the protein s porphyrin and a nearby quinone. Semiempirical methods and QM/MM methods have been developed by Martinez and coworkers " to study the cis-trans isomerization dynamics of the Green Fluorescent Protein chromophore in solution, which occurs through conical intersections.The chromophore in this protein consists of two rings connected with a double bond and has been studied in vacuo as well. ... 

Discuss., 127, 179 (2004). Structure of the Intersection Space Associated with 2/E Photoisomerization of Retinal in Rhodopsin Proteins. 

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