Vitamin A and Vision.

Visual systems detect light by monitoring the effect of photoisomerization of a chromophore on the release of a neurotransmitter from sensory neurons, known as rod and cone photoreceptor cells in vertebrate retina. In all known visual systems, the chromophore is 11-cis-retinal complexed with a protein, called opsin, and photoisomerization produces all-trans-retinal. In mammals, regeneration of 11-cis-retinal following photoisomerization occurs by a thermally driven isomerization reaction.

Vitamin A metabolism in rod and cone visual cycles.

The chromophore of all known visual pigments consists of 11-cis-retinal (derived from either vitamin A1 or A2) or a hydroxylated derivative, bound to a protein (opsin) via a Schiff base. Absorption of a photon results in photoisomerization of the chromophore to all-trans-retinal and conversion of the visual pigment to the signaling form. Regeneration of the 11-cis-retinal occurs in an adjacent tissue and involves several enzymes, several water-soluble retinoid-binding proteins, and intra- and intercellular diffusional processes.

Relationships among visual cycle retinoids, rhodopsin phosphorylation, and phototransduction in mouse eyes during light and dark adaptation.

Phosphorylation and regeneration of rhodopsin, the prototypical G-protein-coupled receptor, each can influence light and dark adaptation. To evaluate their relative contributions, we quantified rhodopsin, retinoids, phosphorylation, and photosensitivity in mice during a 90 min illumination followed by dark adaptation. During illumination, all-trans-retinyl esters and, to a lesser extent, all-trans-retinal accumulate and reach the steady state in <1 h.

Release of 11-cis-retinal from cellular retinaldehyde-binding protein by acidic lipids.

Purpose: To determine molecular mechanisms for the release of 11-cis-retinal from the binding pocket of cellular retinaldehyde-binding protein (CRALBP).

Methods: Binding of CRALBP to lipid surfaces was assessed with a lipid-immunoblot assay. Lipids were presented to CRALBP as small unilamellar vesicles (SUVs) consisting of phosphatidylcholine (PC) plus other lipids.

Localizations of visual cycle components in retinal pigment epithelium.

Purpose: We used immunocytochemistry and confocal microscopy to determine whether enzymes of the rod visual cycle were uniformly distributed in retinal pigment epithelium (RPE) cells. The localizations of these enzymes were compared to known localizations of retinoid-binding proteins and associated proteins.

Methods: Antibodies to proteins and enzymes associated with the rod visual cycle were used for fluorescence immunocytochemistry with frozen sections of albino mouse and rat retina.

Duplication and divergence of zebrafish CRALBP genes uncovers novel role for RPE- and Muller-CRALBP in cone vision.

Purpose: During vertebrate phototransduction 11-cis-retinal is isomerized to all-trans-retinal. Light sensitivity is restored by recombination of apo-opsin with 11-cis-retinal to regenerate visual pigments. The conversion of all-trans retinal back to 11-cis-retinal is known as the visual cycle.

Subunit dissociation and diffusion determine the subcellular localization of rod and cone transducins.

Activation of rod photoreceptors by light induces a massive redistribution of the heterotrimeric G-protein transducin. In darkness, transducin is sequestered within the membrane-enriched outer segments of the rod cell. In light, it disperses throughout the entire neuron.

Scaffold proteins and the regeneration of visual pigments.

CRALBP, cellular retinaldehyde-binding protein, is a retinoid-binding protein necessary for efficient regeneration of rod and cone visual pigments. The C terminus of CRALBP binds to the PDZ domains of EBP50/NHERF-1, which in turn bind to ezrin and actin, proteins localized to the apical processes of the retinal pigment epithelium. In this study, we examined structural features associated with the interaction of the two proteins.

Retinoid processing proteins in the ocular ciliary epithelium.

Purpose: To identify retinoids and retinoid processing proteins in the ocular ciliary epithelium (CE), and to compare in cultured ciliary epithelial cell lines promoter activities of the cellular retinaldehyde binding protein (CRALBP) and interphotoreceptor retinoid binding protein (IRBP).

Methods: Retinoid processing proteins were detected by RT-PCR, western analysis and immunocytochemistry. PCR products were verified by DNA sequence analysis.

Decreased carotenoid content in preaponeurotic orbital fat of patients with involutional ptosis.

Purpose: The underlying cause of involutional blepharoptosis is unknown. The carotenoid content of preaponeurotic and nasal orbital fat among patients with and without involutional ptosis was evaluated to investigate the hypothesis that development of ptosis may be related to low carotenoid content of preaponeurotic orbital fat.

Methods: Through a case-control design, the carotenoid content of preaponeurotic and nasal fat of 10 patients with ptosis and 11 patients without ptosis was measured by spectrophotometry analysis.

Support for a proposed retinoid-processing protein complex in apical retinal pigment epithelium.

The interaction of cellular retinaldehyde-binding protein (CRALBP) with ERM (ezrin, radixin, moesin)-binding phosphoprotein 50 (EBP50) in retinal pigment epithelium (RPE) microsomes has led to the hypothesis that a retinoid-processing protein complex exists in apical RPE. Mouse RPE apical processes were isolated on wheat germ agglutinin-coated agarose beads. Proteomic analyses of the isolated apical RPE demonstrated the presence of CRALBP, EBP50, 11-cis-retinol dehydrogenase, cellular retinol-binding protein 1, and interphotoreceptor retinoid-binding protein.

Cellular retinaldehyde-binding protein interacts with ERM-binding phosphoprotein 50 in retinal pigment epithelium.

Purpose: To characterize mechanisms of apical localization of visual cycle components in retinal pigment epithelium (RPE) by the identification of cellular retinaldehyde-binding protein (CRALBP) interaction partners.

Methods: An overlay assay was used to detect interactions of CRALBP with components of RPE microsomes. Interacting proteins were identified with two-dimensional (2D)-PAGE and liquid chromatography tandem mass spectrometry (LC MS/MS).

Analysis of the visual cycle in cellular retinol-binding protein type I (CRBPI) knockout mice.

Purpose: To determine whether the visual cycle is affected in mice without a functional gene for cellular retinol-binding protein type I (CRBPI(-/-) mice).

Methods: Visual-cycle retinoids and rhodopsin levels were analyzed in eyes of dark adapted (DA) CRBPI(-/-) and wild-type (wt) mice before and during recovery from a flash. The rate of dark adaptation was analyzed using electroretinography (ERG).