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  1. Article ; Online: Dawn and dusk peaks of outer segment phagocytosis, and visual cycle function require Rab28.

    Moran, Ailís L / Carter, Stephen P / Kaylor, Joanna J / Jiang, Zhichun / Broekman, Sanne / Dillon, Eugene T / Gómez Sánchez, Alicia / Minhas, Sajal K / van Wijk, Erwin / Radu, Roxana A / Travis, Gabriel H / Carey, Michelle / Blacque, Oliver E / Kennedy, Breandán N

    FASEB journal : official publication of the Federation of American Societies for Experimental Biology

    2022  Volume 36, Issue 5, Page(s) e22309

    Abstract: RAB28 is a farnesylated, ciliary G-protein. Patient variants in RAB28 are causative of autosomal recessive cone-rod dystrophy (CRD), an inherited human blindness. In rodent and zebrafish models, the absence of Rab28 results in diminished dawn, ... ...

    Abstract RAB28 is a farnesylated, ciliary G-protein. Patient variants in RAB28 are causative of autosomal recessive cone-rod dystrophy (CRD), an inherited human blindness. In rodent and zebrafish models, the absence of Rab28 results in diminished dawn, photoreceptor, outer segment phagocytosis (OSP). Here, we demonstrate that Rab28 is also required for dusk peaks of OSP, but not for basal OSP levels. This study further elucidated the molecular mechanisms by which Rab28 controls OSP and inherited blindness. Proteomic profiling identified factors whose expression in the eye or whose expression at dawn and dusk peaks of OSP is dysregulated by loss of Rab28. Notably, transgenic overexpression of Rab28, solely in zebrafish cones, rescues the OSP defect in rab28 KO fish, suggesting rab28 gene replacement in cone photoreceptors is sufficient to regulate Rab28-OSP. Rab28 loss also perturbs function of the visual cycle as retinoid levels of 11-cRAL, 11cRP, and atRP are significantly reduced in larval and adult rab28 KO retinae (p < .05). These data give further understanding on the molecular mechanisms of RAB28-associated CRD, highlighting roles of Rab28 in both peaks of OSP, in vitamin A metabolism and in retinoid recycling.
    MeSH term(s) Animals ; Blindness/metabolism ; Humans ; Phagocytosis ; Proteomics ; Retinal Cone Photoreceptor Cells/metabolism ; Retinoids/metabolism ; Zebrafish/genetics ; Zebrafish/metabolism ; rab GTP-Binding Proteins/genetics ; rab GTP-Binding Proteins/metabolism
    Chemical Substances Retinoids ; RAB28 protein, human (EC 3.6.1.-) ; rab GTP-Binding Proteins (EC 3.6.5.2)
    Language English
    Publishing date 2022-05-27
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 639186-2
    ISSN 1530-6860 ; 0892-6638
    ISSN (online) 1530-6860
    ISSN 0892-6638
    DOI 10.1096/fj.202101897R
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Non-photopic and photopic visual cycles differentially regulate immediate, early, and late phases of cone photoreceptor-mediated vision.

    Ward, Rebecca / Kaylor, Joanna J / Cobice, Diego F / Pepe, Dionissia A / McGarrigle, Eoghan M / Brockerhoff, Susan E / Hurley, James B / Travis, Gabriel H / Kennedy, Breandán N

    The Journal of biological chemistry

    2020  Volume 295, Issue 19, Page(s) 6482–6497

    Abstract: Cone photoreceptors in the retina enable vision over a wide range of light intensities. However, the processes enabling cone vision in bright light ( ...

    Abstract Cone photoreceptors in the retina enable vision over a wide range of light intensities. However, the processes enabling cone vision in bright light (
    MeSH term(s) Animals ; Carrier Proteins/genetics ; Carrier Proteins/metabolism ; Color Vision ; Ependymoglial Cells/cytology ; Ependymoglial Cells/metabolism ; Fatty Acid Desaturases/genetics ; Fatty Acid Desaturases/metabolism ; Gene Deletion ; Retinal Cone Photoreceptor Cells/cytology ; Retinal Cone Photoreceptor Cells/metabolism ; Vitamin A/genetics ; Vitamin A/metabolism ; Zebrafish/genetics ; Zebrafish/metabolism ; cis-trans-Isomerases/genetics ; cis-trans-Isomerases/metabolism
    Chemical Substances 11-cis-retinal-binding protein ; Carrier Proteins ; Vitamin A (11103-57-4) ; Fatty Acid Desaturases (EC 1.14.19.-) ; retinoid isomerohydrolase (EC 3.1.1.64) ; cis-trans-Isomerases (EC 5.2.-)
    Language English
    Publishing date 2020-04-01
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't
    ZDB-ID 2997-x
    ISSN 1083-351X ; 0021-9258
    ISSN (online) 1083-351X
    ISSN 0021-9258
    DOI 10.1074/jbc.RA119.011374
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Blue light regenerates functional visual pigments in mammals through a retinyl-phospholipid intermediate.

    Kaylor, Joanna J / Xu, Tongzhou / Ingram, Norianne T / Tsan, Avian / Hakobyan, Hayk / Fain, Gordon L / Travis, Gabriel H

    Nature communications

    2017  Volume 8, Issue 1, Page(s) 16

    Abstract: The light absorbing chromophore in opsin visual pigments is the protonated Schiff base of 11-cis-retinaldehyde (11cRAL). Absorption of a photon isomerizes 11cRAL to all-trans-retinaldehyde (atRAL), briefly activating the pigment before it dissociates. ... ...

    Abstract The light absorbing chromophore in opsin visual pigments is the protonated Schiff base of 11-cis-retinaldehyde (11cRAL). Absorption of a photon isomerizes 11cRAL to all-trans-retinaldehyde (atRAL), briefly activating the pigment before it dissociates. Light sensitivity is restored when apo-opsin combines with another 11cRAL to form a new visual pigment. Conversion of atRAL to 11cRAL is carried out by enzyme pathways in neighboring cells. Here we show that blue (450-nm) light converts atRAL specifically to 11cRAL through a retinyl-phospholipid intermediate in photoreceptor membranes. The quantum efficiency of this photoconversion is similar to rhodopsin. Photoreceptor membranes synthesize 11cRAL chromophore faster under blue light than in darkness. Live mice regenerate rhodopsin more rapidly in blue light. Finally, whole retinas and isolated cone cells show increased photosensitivity following exposure to blue light. These results indicate that light contributes to visual-pigment renewal in mammalian rods and cones through a non-enzymatic process involving retinyl-phospholipids.It is currently thought that visual pigments in vertebrate photoreceptors are regenerated exclusively through enzymatic cycles. Here the authors show that mammalian photoreceptors also regenerate opsin pigments in light through photoisomerization of N-ret-PE (N-retinylidene-phosphatidylethanolamine.
    MeSH term(s) Animals ; Apoproteins/genetics ; Apoproteins/metabolism ; Gene Expression Regulation ; Light ; Light Signal Transduction ; Mice ; Opsins/genetics ; Opsins/metabolism ; Phosphatidylethanolamines/metabolism ; Photochemical Processes ; Retinal Cone Photoreceptor Cells/cytology ; Retinal Cone Photoreceptor Cells/metabolism ; Retinal Cone Photoreceptor Cells/radiation effects ; Retinal Rod Photoreceptor Cells/cytology ; Retinal Rod Photoreceptor Cells/metabolism ; Retinal Rod Photoreceptor Cells/radiation effects ; Retinaldehyde/metabolism ; Retinoids/metabolism ; Rhodopsin/genetics ; Rhodopsin/metabolism ; Transducin/genetics ; Transducin/metabolism ; Vision, Ocular/physiology ; Vision, Ocular/radiation effects
    Chemical Substances Apoproteins ; N-retinylidene-phosphatidylethanolamine ; Opsins ; Phosphatidylethanolamines ; Retinoids ; Rhodopsin (9009-81-8) ; Transducin (EC 3.6.5.1) ; Retinaldehyde (RR725D715M)
    Language English
    Publishing date 2017--04
    Publishing country England
    Document type Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't
    ISSN 2041-1723
    ISSN (online) 2041-1723
    DOI 10.1038/s41467-017-00018-4
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Light-Driven Regeneration of Cone Visual Pigments through a Mechanism Involving RGR Opsin in Müller Glial Cells.

    Morshedian, Ala / Kaylor, Joanna J / Ng, Sze Yin / Tsan, Avian / Frederiksen, Rikard / Xu, Tongzhou / Yuan, Lily / Sampath, Alapakkam P / Radu, Roxana A / Fain, Gordon L / Travis, Gabriel H

    Neuron

    2019  Volume 102, Issue 6, Page(s) 1172–1183.e5

    Abstract: While rods in the mammalian retina regenerate rhodopsin through a well-characterized pathway in cells of the retinal pigment epithelium (RPE), cone visual pigments are thought to regenerate in part through an additional pathway in Müller cells of the ... ...

    Abstract While rods in the mammalian retina regenerate rhodopsin through a well-characterized pathway in cells of the retinal pigment epithelium (RPE), cone visual pigments are thought to regenerate in part through an additional pathway in Müller cells of the neural retina. The proteins comprising this intrinsic retinal visual cycle are unknown. Here, we show that RGR opsin and retinol dehydrogenase-10 (Rdh10) convert all-trans-retinol to 11-cis-retinol during exposure to visible light. Isolated retinas from Rgr+/+ and Rgr-/- mice were exposed to continuous light, and cone photoresponses were recorded. Cones in Rgr-/- retinas lost sensitivity at a faster rate than cones in Rgr+/+ retinas. A similar effect was seen in Rgr+/+ retinas following treatment with the glial cell toxin, α-aminoadipic acid. These results show that RGR opsin is a critical component of the Müller cell visual cycle and that regeneration of cone visual pigment can be driven by light.
    MeSH term(s) 2-Aminoadipic Acid/pharmacology ; Alcohol Oxidoreductases/metabolism ; Alcohol Oxidoreductases/radiation effects ; Animals ; Ependymoglial Cells/drug effects ; Ependymoglial Cells/metabolism ; Ependymoglial Cells/radiation effects ; Excitatory Amino Acid Antagonists/pharmacology ; Eye Proteins/genetics ; Eye Proteins/metabolism ; Eye Proteins/radiation effects ; Light ; Mice ; Mice, Knockout ; Receptors, G-Protein-Coupled/genetics ; Receptors, G-Protein-Coupled/metabolism ; Receptors, G-Protein-Coupled/radiation effects ; Retinal Cone Photoreceptor Cells/metabolism ; Retinal Cone Photoreceptor Cells/radiation effects ; Retinal Pigments/metabolism ; Retinal Pigments/radiation effects ; Vitamin A/metabolism
    Chemical Substances Excitatory Amino Acid Antagonists ; Eye Proteins ; G protein-coupled receptor RGR ; Receptors, G-Protein-Coupled ; Retinal Pigments ; Vitamin A (11103-57-4) ; 2-Aminoadipic Acid (1K7B1OED4N) ; Alcohol Oxidoreductases (EC 1.1.-) ; trans-retinol dehydrogenase (EC 1.1.1.-)
    Language English
    Publishing date 2019-05-02
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural ; Research Support, Non-U.S. Gov't
    ZDB-ID 808167-0
    ISSN 1097-4199 ; 0896-6273
    ISSN (online) 1097-4199
    ISSN 0896-6273
    DOI 10.1016/j.neuron.2019.04.004
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Analysis of the retinoid isomerase activities in the retinal pigment epithelium and retina.

    Travis, Gabriel H / Kaylor, Joanna / Yuan, Quan

    Methods in molecular biology (Clifton, N.J.)

    2010  Volume 652, Page(s) 329–339

    Abstract: Light sensitivity in the vertebrate retina is mediated by the opsin visual pigments inside rod and cone photoreceptor cells. These pigments consist of a G protein-coupled receptor and the photo-sensitive ligand, 11-cis-retinaldehyde (11-cis-RAL). ... ...

    Abstract Light sensitivity in the vertebrate retina is mediated by the opsin visual pigments inside rod and cone photoreceptor cells. These pigments consist of a G protein-coupled receptor and the photo-sensitive ligand, 11-cis-retinaldehyde (11-cis-RAL). Absorption of a photon by an opsin pigment induces isomerization of the 11-cis-RAL chromophore to all-trans-retinaldehyde (all-trans-RAL), rendering the pigment insensitive to light. The bleached opsin regains light sensitivity by recombining with another 11-cis-RAL. The vertebrate eye contains a biochemical mechanism for regenerating 11-cis-RAL chromophore from all-trans-RAL, called the visual cycle. The visual cycle takes place within cells of the retinal pigment epithelium (RPE). A second visual cycle also appears to be present in Müller glial cells of the retina. A critical step in the regeneration of 11-cis-RAL chromophore is thermal re-isomerization to the 11-cis configuration of an all-trans-retinyl ester (all-trans-RE) or an all-trans-retinol (all-trans-ROL). In RPE cells, this step is carried out by an enzyme called Rpe65 isomerase. This chapter provides methods for assaying Rpe65 isomerase. Although Rpe65 utilizes an all-trans-RE such as all-trans-retinyl palmitate (all-trans-RP) as substrate, it can be assayed in RPE homogenates by providing all-trans-ROL substrate and allowing the endogenous lecithin:retinol acyl transferase (LRAT) to synthesize all-trans-REs using fatty acids from phosphatidylcholine in the membranes. Alternatively, all-trans-RP can be provided directly as substrate, although this requires the isomerase reaction to be carried out in the presence of detergent, since fatty-acyl esters of all-trans-ROL are insoluble. Methods are provided in this chapter for assaying Rpe65 in RPE homogenates with both all-trans-ROL and all-trans-RP substrates. A second visual cycle appears to be present in the retinas of cone-dominant species such as chicken. This retinal pathway may augment the RPE to provide 11-cis-RAL to cone photoreceptors under conditions of bright light where the rate of opsin photoisomerization is high. The isomerase in this pathway (isomerase-2) utilizes all-trans-ROL and palmitoyl coenzyme A (palm CoA) as substrates to synthesize 11-cis-retinyl palmitate (11-cis-RP). Isomerase-2 appears to be present in Müller cells but has not yet been identified. Methods are provided in this chapter for assaying isomerase-2 in chicken retina homogenates.
    MeSH term(s) Animals ; Cattle ; Chickens ; Chromatography, Liquid ; Diterpenes ; Enzyme Assays/methods ; Retinal Pigment Epithelium/enzymology ; Retinyl Esters ; Vitamin A/analogs & derivatives ; Vitamin A/metabolism ; cis-trans-Isomerases/metabolism
    Chemical Substances Diterpenes ; Retinyl Esters ; Vitamin A (11103-57-4) ; retinol palmitate (1D1K0N0VVC) ; retinoid isomerohydrolase (EC 3.1.1.64) ; cis-trans-Isomerases (EC 5.2.-)
    Language English
    Publishing date 2010-06-16
    Publishing country United States
    Document type Journal Article
    ISSN 1940-6029
    ISSN (online) 1940-6029
    DOI 10.1007/978-1-60327-325-1_19
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  6. Article ; Online: Identification of the 11-cis-specific retinyl-ester synthase in retinal Müller cells as multifunctional O-acyltransferase (MFAT).

    Kaylor, Joanna J / Cook, Jeremy D / Makshanoff, Jacob / Bischoff, Nicholas / Yong, Jennifer / Travis, Gabriel H

    Proceedings of the National Academy of Sciences of the United States of America

    2014  Volume 111, Issue 20, Page(s) 7302–7307

    Abstract: Absorption of a photon by a rhodopsin or cone-opsin pigment isomerizes its 11-cis-retinaldehyde (11-cis-RAL) chromophore to all-trans-retinaldehyde (all-trans-RAL), which dissociates after a brief period of activation. Light sensitivity is restored to ... ...

    Abstract Absorption of a photon by a rhodopsin or cone-opsin pigment isomerizes its 11-cis-retinaldehyde (11-cis-RAL) chromophore to all-trans-retinaldehyde (all-trans-RAL), which dissociates after a brief period of activation. Light sensitivity is restored to the resulting apo-opsin when it recombines with another 11-cis-RAL. Conversion of all-trans-RAL to 11-cis-RAL is carried out by an enzyme pathway called the visual cycle in cells of the retinal pigment epithelium. A second visual cycle is present in Müller cells of the retina. The retinol isomerase for this noncanonical pathway is dihydroceramide desaturase (DES1), which catalyzes equilibrium isomerization of retinol. Because 11-cis-retinol (11-cis-ROL) constitutes only a small fraction of total retinols in an equilibrium mixture, a subsequent step involving selective removal of 11-cis-ROL is required to drive synthesis of 11-cis-retinoids for production of visual chromophore. Selective esterification of 11-cis-ROL is one possibility. Crude homogenates of chicken retinas rapidly convert all-trans-ROL to 11-cis-retinyl esters (11-cis-REs) with minimal formation of other retinyl-ester isomers. This enzymatic activity implies the existence of an 11-cis-specific retinyl-ester synthase in Müller cells. Here, we evaluated multifunctional O-acyltransferase (MFAT) as a candidate for this 11-cis-RE-synthase. MFAT exhibited much higher catalytic efficiency as a synthase of 11-cis-REs versus other retinyl-ester isomers. Further, we show that MFAT is expressed in Müller cells. Finally, homogenates of cells coexpressing DES1 and MFAT catalyzed the conversion of all-trans-ROL to 11-cis-RP, similar to what we observed with chicken-retina homogenates. MFAT is therefore an excellent candidate for the retinyl-ester synthase that cooperates with DES1 to drive synthesis of 11-cis-retinoids by mass action.
    MeSH term(s) Acetyltransferases/metabolism ; Animals ; Catalysis ; Cattle ; Chickens ; Cone Opsins/metabolism ; Ependymoglial Cells/enzymology ; Esters/chemistry ; Fatty Acids/chemistry ; Gene Expression Profiling ; Gene Expression Regulation, Enzymologic ; HEK293 Cells ; Humans ; Kinetics ; Mice ; Multifunctional Enzymes/metabolism ; Opsins/metabolism ; Retina/metabolism ; Retinol O-Fatty-Acyltransferase/metabolism
    Chemical Substances Cone Opsins ; Esters ; Fatty Acids ; Multifunctional Enzymes ; Opsins ; Acetyltransferases (EC 2.3.1.-) ; Retinol O-Fatty-Acyltransferase (EC 2.3.1.76)
    Language English
    Publishing date 2014-05-05
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural
    ZDB-ID 209104-5
    ISSN 1091-6490 ; 0027-8424
    ISSN (online) 1091-6490
    ISSN 0027-8424
    DOI 10.1073/pnas.1319142111
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  7. Article ; Online: Blue light regenerates functional visual pigments in mammals through a retinyl-phospholipid intermediate

    Joanna J. Kaylor / Tongzhou Xu / Norianne T. Ingram / Avian Tsan / Hayk Hakobyan / Gordon L. Fain / Gabriel H. Travis

    Nature Communications, Vol 8, Iss 1, Pp 1-

    2017  Volume 10

    Abstract: It is currently thought that visual pigments in vertebrate photoreceptors are regenerated exclusively through enzymatic cycles. Here the authors show that mammalian photoreceptors also regenerate opsin pigments in light through photoisomerization of N- ... ...

    Abstract It is currently thought that visual pigments in vertebrate photoreceptors are regenerated exclusively through enzymatic cycles. Here the authors show that mammalian photoreceptors also regenerate opsin pigments in light through photoisomerization of N-ret-PE (N-retinylidene-phosphatidylethanolamine.
    Keywords Science ; Q
    Language English
    Publishing date 2017-05-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  8. Article ; Online: Diacylglycerol O-acyltransferase type-1 synthesizes retinyl esters in the retina and retinal pigment epithelium.

    Kaylor, Joanna J / Radu, Roxana A / Bischoff, Nicholas / Makshanoff, Jacob / Hu, Jane / Lloyd, Marcia / Eddington, Shannan / Bianconi, Tran / Bok, Dean / Travis, Gabriel H

    PloS one

    2015  Volume 10, Issue 5, Page(s) e0125921

    Abstract: Retinyl esters represent an insoluble storage form of vitamin A and are substrates for the retinoid isomerase (Rpe65) in cells of the retinal pigment epithelium (RPE). The major retinyl-ester synthase in RPE cells is lecithin:retinol acyl-transferase ( ... ...

    Abstract Retinyl esters represent an insoluble storage form of vitamin A and are substrates for the retinoid isomerase (Rpe65) in cells of the retinal pigment epithelium (RPE). The major retinyl-ester synthase in RPE cells is lecithin:retinol acyl-transferase (LRAT). A second palmitoyl coenzyme A-dependent retinyl-ester synthase activity has been observed in RPE homogenates but the protein responsible has not been identified. Here we show that diacylglycerol O-acyltransferase-1 (DGAT1) is expressed in multiple cells of the retina including RPE and Müller glial cells. DGAT1 catalyzes the synthesis of retinyl esters from multiple retinol isomers with similar catalytic efficiencies. Loss of DGAT1 in dgat1(-/-) mice has no effect on retinal anatomy or the ultrastructure of photoreceptor outer-segments (OS) and RPE cells. Levels of visual chromophore in dgat1(-/-) mice were also normal. However, the normal build-up of all-trans-retinyl esters (all-trans-RE's) in the RPE during the first hour after a deep photobleach of visual pigments in the retina was not seen in dgat1(-/-) mice. Further, total retinyl-ester synthase activity was reduced in both dgat1(-/-) retina and RPE.
    MeSH term(s) Acyltransferases/metabolism ; Animals ; Cells, Cultured ; Diacylglycerol O-Acyltransferase/analysis ; Diacylglycerol O-Acyltransferase/genetics ; Diacylglycerol O-Acyltransferase/metabolism ; Esters/metabolism ; Gene Deletion ; Mice, Inbred BALB C ; Mice, Inbred C57BL ; Palmitoyl Coenzyme A/metabolism ; Retina/cytology ; Retina/metabolism ; Retina/ultrastructure ; Retinal Pigment Epithelium/cytology ; Retinal Pigment Epithelium/metabolism ; Retinal Pigment Epithelium/ultrastructure ; Retinaldehyde/metabolism ; Vitamin A/metabolism ; cis-trans-Isomerases/metabolism
    Chemical Substances Esters ; Vitamin A (11103-57-4) ; Palmitoyl Coenzyme A (1763-10-6) ; Acyltransferases (EC 2.3.-) ; lecithin-retinol acyltransferase (EC 2.3.1.-) ; Diacylglycerol O-Acyltransferase (EC 2.3.1.20) ; retinoid isomerohydrolase (EC 3.1.1.64) ; cis-trans-Isomerases (EC 5.2.-) ; Retinaldehyde (RR725D715M)
    Language English
    Publishing date 2015
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural
    ISSN 1932-6203
    ISSN (online) 1932-6203
    DOI 10.1371/journal.pone.0125921
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  9. Article ; Online: Rpe65 isomerase associates with membranes through an electrostatic interaction with acidic phospholipid headgroups.

    Yuan, Quan / Kaylor, Joanna J / Miu, Anh / Bassilian, Sara / Whitelegge, Julian P / Travis, Gabriel H

    The Journal of biological chemistry

    2009  Volume 285, Issue 2, Page(s) 988–999

    Abstract: Opsins are light-sensitive pigments in the vertebrate retina, comprising a G protein-coupled receptor and an 11-cis-retinaldehyde chromophore. Absorption of a photon by an opsin pigment induces isomerization of its chromophore to all-trans-retinaldehyde. ...

    Abstract Opsins are light-sensitive pigments in the vertebrate retina, comprising a G protein-coupled receptor and an 11-cis-retinaldehyde chromophore. Absorption of a photon by an opsin pigment induces isomerization of its chromophore to all-trans-retinaldehyde. After a brief period of activation, opsin releases all-trans-retinaldehyde and becomes insensitive to light. Restoration of light sensitivity to the apo-opsin involves the conversion of all-trans-retinaldehyde back to 11-cis-retinaldehyde via an enzyme pathway called the visual cycle. The critical isomerization step in this pathway is catalyzed by Rpe65. Rpe65 is strongly associated with membranes but contains no membrane-spanning segments. It was previously suggested that the affinity of Rpe65 for membranes is due to palmitoylation of one or more Cys residues. In this study, we re-examined this hypothesis. By two independent strategies involving mass spectrometry, we show that Rpe65 is not palmitoylated nor does it appear to undergo other post-translational modifications at significant stoichiometry. Instead, we show that Rpe65 binds the acidic phospholipids, phosphatidylserine, phosphatidylglycerol, and cardiolipin, but not phosphatidic acid. No binding of Rpe65 to basic phospholipids or neutral lipids was observed. The affinity of Rpe65 to acidic phospholipids was strongly pH-dependent, suggesting an electrostatic interaction of basic residues in Rpe65 with negatively charged phospholipid headgroups. Binding of Rpe65 to liposomes containing phosphatidylserine or phosphatidylglycerol, but not the basic or neutral phospholipids, allowed the enzyme to extract its insoluble substrate, all-trans-retinyl palmitate, from the lipid bilayer for synthesis of 11-cis-retinol. The interaction of Rpe65 with acidic phospholipids is therefore biologically relevant.
    MeSH term(s) Animals ; Carrier Proteins/chemistry ; Carrier Proteins/genetics ; Carrier Proteins/metabolism ; Cattle ; Cell Membrane/chemistry ; Cell Membrane/genetics ; Cell Membrane/metabolism ; Chickens ; Eye Proteins/chemistry ; Eye Proteins/genetics ; Eye Proteins/metabolism ; Hydrogen-Ion Concentration ; Isomerism ; Lipid Bilayers/chemistry ; Lipid Bilayers/metabolism ; Opsins/genetics ; Opsins/metabolism ; Palmitic Acid/metabolism ; Phospholipids/chemistry ; Phospholipids/genetics ; Phospholipids/metabolism ; Protein Binding/physiology ; Protein Processing, Post-Translational/physiology ; Retinaldehyde/genetics ; Retinaldehyde/metabolism ; Static Electricity
    Chemical Substances Carrier Proteins ; Eye Proteins ; Lipid Bilayers ; Opsins ; Phospholipids ; Palmitic Acid (2V16EO95H1) ; Retinaldehyde (RR725D715M)
    Language English
    Publishing date 2009-11-05
    Publishing country United States
    Document type Journal Article ; Research Support, N.I.H., Extramural
    ZDB-ID 2997-x
    ISSN 1083-351X ; 0021-9258
    ISSN (online) 1083-351X
    ISSN 0021-9258
    DOI 10.1074/jbc.M109.025643
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Article ; Online: Diacylglycerol O-acyltransferase type-1 synthesizes retinyl esters in the retina and retinal pigment epithelium.

    Joanna J Kaylor / Roxana A Radu / Nicholas Bischoff / Jacob Makshanoff / Jane Hu / Marcia Lloyd / Shannan Eddington / Tran Bianconi / Dean Bok / Gabriel H Travis

    PLoS ONE, Vol 10, Iss 5, p e

    2015  Volume 0125921

    Abstract: Retinyl esters represent an insoluble storage form of vitamin A and are substrates for the retinoid isomerase (Rpe65) in cells of the retinal pigment epithelium (RPE). The major retinyl-ester synthase in RPE cells is lecithin:retinol acyl-transferase ( ... ...

    Abstract Retinyl esters represent an insoluble storage form of vitamin A and are substrates for the retinoid isomerase (Rpe65) in cells of the retinal pigment epithelium (RPE). The major retinyl-ester synthase in RPE cells is lecithin:retinol acyl-transferase (LRAT). A second palmitoyl coenzyme A-dependent retinyl-ester synthase activity has been observed in RPE homogenates but the protein responsible has not been identified. Here we show that diacylglycerol O-acyltransferase-1 (DGAT1) is expressed in multiple cells of the retina including RPE and Müller glial cells. DGAT1 catalyzes the synthesis of retinyl esters from multiple retinol isomers with similar catalytic efficiencies. Loss of DGAT1 in dgat1(-/-) mice has no effect on retinal anatomy or the ultrastructure of photoreceptor outer-segments (OS) and RPE cells. Levels of visual chromophore in dgat1(-/-) mice were also normal. However, the normal build-up of all-trans-retinyl esters (all-trans-RE's) in the RPE during the first hour after a deep photobleach of visual pigments in the retina was not seen in dgat1(-/-) mice. Further, total retinyl-ester synthase activity was reduced in both dgat1(-/-) retina and RPE.
    Keywords Medicine ; R ; Science ; Q
    Subject code 570
    Language English
    Publishing date 2015-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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