Photoreceptor proteins

Mutations in rhodopsin and other photoreceptor proteins are linked to retinitis pigmentosa 814... 

Mutations in rhodopsin and other photoreceptor proteins are linked to retinitis pigmentosa. Retinitis pigmentosa (RP) is a group of inherited retinopathies that affects about 1 in 4,000 humans [26], RP maybe classified into four types autosomal dominant (19%), autosomal recessive (19%),X-linked (8%) and allied diseases (54%). RP is characterized by loss of night vision in the early stage, followed by loss of peripheral vision. Chromosomal loci for numerous RP genes have been mapped and mutations characterized [27]. 

Ishikawa T, Matsumoto A, Kato T Jr et al 1999 dCRY is a Drosophila photoreceptor protein implicated in light entrainment of circadian rhythm. Genes Cells 4 57—65... 

Matsubara S, Yamaji Y, Sato M, Fujita J, Takahara J. Expression of a photoreceptor protein, recoverin, as a cancer-associated retinopathy autoantigen in human lung cancer cell lines. Br J Cancer 1996 74(9) 1419-1422. 

In contrast, proteins vary markedly in their lateral mobility. Some proteins are nearly as mobile as lipids, whereas others are virtually immobile. For example, the photoreceptor protein rhodopsin (Section 32.3.1). a very mobile protein, has a diffusion coefficient of 0.4 pm s f The rapid movement of rhodopsin is essential for fast signaling. At the other extreme is fibronectin, a peripheral glycoprotein that interacts with the extracellular matrix. For fibronectin, D is less than 10-4 pm2 s f Fibronectin has a very low mobility because it is anchored to actin filaments on the inside of the plasma membrane through integrin, a transmembrane protein that links the extracellular matrix to the cytoskeleton. 

Cone cells, like rod cells, contain visual pigments. Like rhodopsin, these photoreceptor proteins are members of the 7TM receptor family and utilize 11-cA-retinal as their chromophore. In human cone cells, there are three distinct photoreceptor proteins with absorption maxima at 426, 530, and 560 nm (Figure 32.26). These absorbances correspond to (in fact, define) the blue, green, and red regions of the spectrum. Recall that the absorption maximum for rhodopsin is 500 nm. 

Figure 32.29. Recombination Pathways Leading to Color Blindness. Rearrangements in the course of DNA replication may lead to (A) the loss of visual pigment genes or (B) the formation of hybrid pigment genes that encode photoreceptors with anomolous absorption spectra. Because the amino acids most important for determining absorption spectra are in the carboxyl-terminal half of each photoreceptor protein, the part of the gene that encodes this region most strongly affects the absorption characteristics of hybrid receptors. [Adapted from J. Nathans. Neuron 24(1999) 299-312 by permission of Cell Press.]...

A section on protein structural chemistry in archaea includes Chapters 5 through 7, respectively, by D. Oesterhelt on the structure and function of photoreceptor proteins in the Halobacteriaceae J. Lanyi on the structure and function of ion-transport rhodopsins in extreme halophiles and R. Hensel on proteins of extreme thermophiles. In a section on cell envelopes (Chapters 8-10), O. Kandler and H. Konig discuss the structure and chemistry of archaeal cell walls M. Kates reviews the chemistry and function of membrane lipids of archaea and L.I. Hochstein covers membrane-bound proteins (enzymes) in archaea. 

Van der Horst MA, HeUingwerf KJ (2004) Photoreceptor proteins, star actors of modem times a review of the functional dynamics in the stmcture of representative members of six different photoreceptor famdies. Acc Chem Res 37 13-20... 

ABC-B (11) photoreceptor proteins Efflux transporters, multiple drug MDR, TAP, Epithelial cells, tumor cells... 

Other proteins that have activities that correlate with the mesomorphic tendencies of the lipid bilayer include the vertebrate photoreceptor protein rhodopsin (42) and a dolichylphosphomannose synthase (43). The paucity of other examples reflects the lack of systematic studies. Membrane protein reconstitutions are generally difficult to perform, especially if the lipid composition is to be varied, and, therefore, are unlikely to be undertaken without good reason. Studies of correlations with lipid mesomorphic tendencies, stimulated by research such as that reported here, are now under consideration by several biochemical groups. Certainly, much more work is needed in this area. 

All retinal-dependent visual pigments form Schiff bases with lysine side chains of the photoreceptor proteins. How can the same chromophore be "tuned" to absorb across the wavelength range of 360 to 635 nm Modern techniques such as resonance Ra-man and FTIR spectroscopies and study of mutant forms have shown that interaction of the conjugated double bond system of the chromophores with immediately adjacent dipoles of side chain groups and peptide linkages is sufficient to account for the great variability in absorption maxima. 

The first step in the light-activated isomerization of retinal in the visual photoreceptor protein, rhodopsin, occurs in less than 6 ps. How far would a beam of light travel in this time ... 

Matsumoto, H. and Komori N., 2000, Ocular proteomics cataloging photoreceptor proteins by two-dimensional gel electrophoresis and mass spectrometry. Methods Enzymol. 316 492-511. 

---