P-Rhodopsin

Sakmar, T.P., Rhodopsin a prototypical G protein-coupled receptor. Prog. Nucleic Acid Res. Mol Biol, 59, 1, 1998. 

Two molecules of vitamin A are formed from one molecule of -carotene. Vitamin A crystallizes in pale yellow needles m.p. 64 C. It is optically inactive. It is unstable in solution when heated in air, but comparatively stable without aeration. Vitamin A is manufactured by extraction from fish-liver oils and by synthesis from / -ionone. The role of vitamin A in vision seems to be different from its systemic function. See also relincne and rhodopsin. 

Shreve A P and Mathies R A 1995 Thermal effects in resonance Raman-scattering—analysis of the Raman intensities of rhodopsin and of the time-resolved Raman-scattering of bacteriorhodopsin J. Phys. Chem. 99 7285-99... 

The G-proteins are heterotrimers made of three families of subunits, a, P, and y, which can interact specifically with discrete regions on G-protein-coupled receptors. This includes most receptors for neurotransmitters and polypeptide hormones (see Neuroregulators). G-protein-coupled receptors also embrace the odorant receptor family and the rhodopsin-linked visual cascade. 

Kniep R, Simon P (2007) Fluorapatite-Gelatine-Nanocomposites Self-Organized Morphogenesis, Real Structure and Relations to Natural Hard Materials. 270 73-125 Koenig BW (2007) Residual Dipolar Couplings Report on the Active Conformation of Rhodopsin-Bound Protein Fragments. 272 187-216 Kolusheva S, see Jelinek R (2007) 277 155-180... 

The effect of receptor stimulation is thus to catalyze a reaction cycle. This leads to considerable amplification of the initial signal. For example, in the process of visual excitation, the photoisomerization of one rhodopsin molecule leads to the activation of approximately 500 to 1000 transdudn (Gt) molecules, each of which in turn catalyzes the hydrolysis of many hundreds of cyclic guanosine monophosphate (cGMP) molecules by phosphodiesterase. Amplification in the adenylate cyclase cascade is less but still substantial each ligand-bound P-adrenoceptor activates approximately 10 to 20 Gs molecules, each of which in turn catalyzes the production of hundreds of cyclic adenosine monophosphate (cAMP) molecules by adenylate cyclase. 

Rhodopsin is a seven ot-helix trans-membrane protein and visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In this photoreceptor, retinal is the chromophore bound by opsin protein, covalently linked to Lys296 by a Schiff base linkage. Kpega et al.64 have studied NMR spectra of Schiff bases being derivatives of all-frans retinal and amino-p-cyclodextrins as a model of rhodopsin, where p-cyclodextrin plays a role of a binding pocket. On the basis of analysis of the chemical shift differences for the model compound in the presence and in the absence of adamantane carboxylate, it has been shown that the derivative of 3-amino-p-cyclodextrin forms dimer in water and retinoid is inserted into p-cyclodextrin cavity [31]. 

Jacobsen, R.B., Sale, K.L., Ayson, M.J., Novak, P., Hong, J., Lane, P., Wood, N.L., Kruppa, G.H., Young, M.M., and Schoeniger, J.S. (2006) Structure and dynamics of dark-state bovine rhodopsin revealed by chemical cross-linking and high-resolution mass spectrometry. Protein Sci. 15, 1303-1317. 

Sheikh, S. P, Zvyaga, T. A., Lichtarge, O., Sakmar, T. P., and Bourne, H. R. (1996) Rhodopsin activation blocked by metal-ion-binding sites linking transmembrane helices C and F. Nature 383, 347-350. 

Huang, P., Visiers, I., Weinstein, H., and Fiu-Chen, F.-Y. (2002) The local environment at the cytoplasmic end of TM6 of the m opioid receptor dilfers from those of rhodopsin and monoamine receptors introduction of an ionic lock between the cytoplasmic ends of helices 3 and 6 by a L6.30(275)E mutation inactivates the m opioid receptor and reduces the constitutive activity of its Thr6.34(279)K mutant. Biochemistry 41, 11972-11980. 

Krishna, A. G., Menon, S. T., Terry, T. J., and Sakmar, T. P. (2002) Evidence that helix 8 of rhodopsin acts as a membrane-dependent conformational switch. Biochemistry 41, 8298-8309. 

Lin, S. W. and Sakmar, T. P. (1996) Specific tryptophan UV-absorbance changes are probes of the transition of rhodopsin to its active state. Biochemistry 35,11149-11159. 

Krebs, A., Villa, C., Edwards, P. C., and Schertler, G. F. (1998) Characterisation of an improved two-dimensional p22121 crystal from bovine rhodopsin. J. Mol. Biol. 282, 991-1003. 

Schertler, G. F. and Hargrave, P. A. (1995) Projection structure of frog rhodopsin in two crystal forms. Proc. Natl. Acad. Sci. USA 92,11578-11582. 

Sullivan, L. J., Makris, G. S., Dickinson, P., et al. (1993) A new codon 15 rhodopsin gene mutation in autosomal-dominant retinitis-pigmentosa is associated with sectorial disease. Arch. Ophthalmol. Ill, 1512-1517. 

Farrar, G. J., Mcwffliam, P., Bradley, D. G., et al. (1990) Autosomal dominant retinitis-pigmentosa— Unkage to rhodopsin and evidence for genetic-heterogeneity. Genomics. 8,35-40. 

Proton gradients can be built up in various ways. A very unusual type is represented by bacteriorhodopsin (1), a light-driven proton pump that various bacteria use to produce energy. As with rhodopsin in the eye, the light-sensitive component used here is covalently bound retinal (see p. 358). In photosynthesis (see p. 130), reduced plastoquinone (QH2) transports protons, as well as electrons, through the membrane (Q cycle, 2). The formation of the proton gradient by the respiratory chain is also coupled to redox processes (see p. 140). In complex III, a Q,cycle is responsible for proton translocation (not shown). In cytochrome c oxidase (complex IV, 3), trans-... 

The cell illustrated opposite, a rod, has a structure divided by membrane discs into which the 7-helix receptor rhodopsin is integrated (see p. 224). In contrast to other receptors in the 7-helix class (see p. 384), rhodopsin is a light-sensitive chromoprotein. Its protein part, opsin, contains the aldehyde retinal (see p. 364)—an isoprenoid which is bound to the e-amino group of a lysine residue as an aldimine. 

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