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Micronutrients
Published in Chuong Pham-Huy, Bruno Pham Huy, Food and Lifestyle in Health and Disease, 2022
Chuong Pham-Huy, Bruno Pham Huy
Retinal, the aldehyde form of vitamin A, is a cofactor for opsin, an apoprotein in the eye. Opsins are responsible for dim-light vision in the rods (rhodopsin) and are involved in color and bright-light vision in the cone of the retina (iodopsin). Retinoic acid is the metabolite form of vitamin A that regulates genes. It binds to proteins called retinoic acid receptors (RARs) and retinoid X receptors (RXRs). These proteins are transcription factors belonging to the steroid/thyroid hormone receptor superfamily of proteins and are found throughout the body. The RAR/RXR proteins regulate the transcription of numerous target genes important for cell development (90).
The vitamins
Published in Geoffrey P. Webb, Nutrition, 2019
Rhodopsin is the light-sensitive pigment in the rod cells of the retina. It is comprised of 11-cis retinal (the chromophore) and a protein called opsin. Within the eye, all trans retinol (vitamin A) is converted by enzymes to 11-cis retinal and this binds spontaneously with opsin to form rhodopsin. Light induces isomerisation of the 11-cis retinal in rhodopsin to all trans retinal, and this causes the opsin and retinal to dissociate and the pigment to become bleached. It is this light-induced cis-to-trans isomerisation that generates the nervous impulses that we perceive as vision. Enzymes in the eye then regenerate 11-cis retinal and thus rhodopsin (summarised in Figure 15.2).
Neuroenhancement and Therapy in National Defense Contexts
Published in L. Syd M Johnson, Karen S. Rommelfanger, The Routledge Handbook of Neuroethics, 2017
Michael N. Tennison, Jonathan D. Moreno
Stimulating and modulating the brain with electricity, electromagnetism, and ultrasound may end up treating and enhancing a vast array of cognitive capacities related to learning and memory, but all of these techniques lack the ability to selectively target certain kinds of neurons while leaving others unaffected. Genes, on the other hand, produce proteins unique to certain kinds of cells and therefore hold promise for researchers to understand and ultimately intervene at the level of individual neurons and their pathways. A new laboratory system called optogenetics entails tagging particular neuronal systems with opsins, a type of light-sensitive protein, to visualize and manipulate neuronal activity (Tye and Deisseroth, 2012). By inserting opsin-producing genes, neurons in the brain can be activated or blocked with fiber-optic light. This kind of precise control over individual neurons opens up many areas of research. For example, in the laboratory, light-sensitive proteins have conditioned rodents for fear responses (Liu et al., 2012), the ventromedial hypothalamus to stimulate mating and aggression (Lin et al., 2011), and the spiral ganglion to reverse hearing loss (Hernandez et al., 2014). Optogenetics is far from experimentation in human subjects, but the implication is clear: optogenetics is a powerful and precise method for learning about the brain and for the control of certain behaviors and capabilities, information that may someday lead to new modalities for neurological management and enhancement.
An in silico toolbox for the prediction of the potential pathogenic effects of missense mutations in the dimeric region of hRPE65
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2023
Giulio Poli, Gian Carlo Demontis, Andrea Sodi, Alessandro Saba, Stanislao Rizzo, Marco Macchia, Tiziano Tuccinardi
Opsins are a group of G protein-coupled receptors capable of capturing photons and thus initiate visual perception in rod and cone photoreceptors of the retina, using 11-cis-retinaldehyde (11-cis-RAL) as a chromophore1. Absorption of a photon by a rod- or cone-opsin pigment induces isomerisation of 11-cis-RAL to all-trans-retinaldehyde (all-trans-RAL) that dissociates from the bleached pigment, rendering it insensitive to light. To restore light-sensitivity, the all-trans-RAL is subjected to a multistep process termed retinoid visual cycle that reisomerize it to 11-cis-RAL, which recombines with apo-opsin to form a new pigment molecule.2 The first catalytic step of the visual cycle is the reduction in photoreceptors of all-trans-RAL to all-trans-retinol (all-trans-ROL) that is released from the photoreceptors and is esterificated by lecithin:retinol acyltransferase (LRAT) to all-trans-retinyl esters (all-trans-RE) in the retinal pigment epithelium (RPE). Then, the retinal pigment epithelium 65 kDa protein (RPE65) catalyses the trans-cis isomerisation reaction, taking all-trans-RE as substrates and converting them, through hydrolysis and alkene isomerisation, into 11-cis-retinol (11-cis-ROL) that is finally oxidised to 11-cis-RAL by 11-cis-retinol dehydrogenase enzymes and then shuttled back to photoreceptors to regenerate ground-state visual pigments3.
Predicting potentially pathogenic effects of hRPE65 missense mutations: a computational strategy based on molecular dynamics simulations
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2022
Giulio Poli, Ivana Barravecchia, Gian Carlo Demontis, Andrea Sodi, Alessandro Saba, Stanislao Rizzo, Marco Macchia, Tiziano Tuccinardi
Photon capture by opsins, a group of proteins belonging to the G protein-coupled receptor superfamily, starts visual perception in rod and cone photoreceptors of the vertebrate retina. Rod and cone opsins require 11-cis-retinaldehyde (11-cis-RAL) as a chromophore to operate as light sensors1. Photon absorption triggers 11-cis-RAL rapid isomerisation to all-trans retinaldehyde (all-trans-RAL), eventually dissociating into opsin and free all-trans-RAL2. Visual pigment regeneration represents a critical step in keeping photoreceptors responsive to light. For this purpose, the all-trans-RAL must be efficiently recycled via isomerisation in all-cis-RAL by a multistep process termed retinoid visual cycle, which involves several enzymatic steps3. The all-trans-RAL is initially reduced to all-trans-retinol (all-trans-ROL), the substrate for lecithin:retinol acyltransferase (LRAT), which catalyses the esterification of all-trans-ROL to all-trans-retinyl esters (all-trans-RE) in the retinal pigment epithelium (RPE). The all-trans-RE are then isomerised and hydrolysed to 11-cis-retinol (11-cis-ROL) by the retinal pigment epithelium-specific 65-kDa protein (RPE65), an isomerohydrolase enzyme4. Finally, 11-cis-ROL oxidation to 11-cis-retinal and its export from RPE cells to photoreceptors regenerates the visual pigment.
Visual and ocular findings in a family with X-linked cone dysfunction and protanopia
Published in Ophthalmic Genetics, 2021
Dag Holmquist, David Epstein, Monica Olsson, Bernd Wissinger, Susanne Kohl, Jürg Hengstler, Kristina Tear-Fahnehjelm
BED was first reported in 1988 in a single large family originating from the Danish island of Bornholm where the family members had high myopia and astigmatism, impaired visual acuity, signs of optic nerve head hypoplasia, abnormal cone electroretinography (ERG) and deutan color vision defect (1). In 1990, the phenotype was mapped to the tip of the q-arm of the X-chromosome at Xq28 by linkage analysis and became the first locus identified for high myopia (MYP1) (2). Xq28 contains the long- (L, “red”) and middle-wavelength (M, “green”) sensitive opsin gene array, harbouring the OPN1LW and OPN1MW genes, respectively. Studies have identified common gene rearrangements, deletions and point mutations at the opsin gene array accounting for cone photoreceptor dysfunction and color vision defects, namely protanopia, deuteranopia for the commonly known “red-green color blindness” but also blue cone monochromatism (BCM), a retinal disease with non-functional L and M cones (3).