ZFIN ID: ZDB-PUB-110628-34
An Alternative Isomerohydrolase in the Retinal Müller Cells of a Cone-Dominant Species
Takahashi, Y., Moiseyev, G., Chen, Y., Nikolaeva, O., and Ma, J.X.
Date: 2011
Source: The FEBS journal 278(16): 2913-26 (Journal)
Registered Authors:
Keywords: retinoids, cone-dominant retina, isomerohydrolase, Müller cell, visual cycle
MeSH Terms:
  • Animals
  • Iron/physiology
  • Kinetics
  • Retinal Cone Photoreceptor Cells/enzymology*
  • Retinal Rod Photoreceptor Cells/enzymology
  • Vitamin A/metabolism
  • Zebrafish
  • cis-trans-Isomerases/metabolism*
PubMed: 21676174 Full text @ FEBS J.
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ABSTRACT
Cone photoreceptors have faster light responses than rods and a higher demand for 11-cis retinal (11cRAL), the chromophore of visual pigments. RPE65 is the isomerohydrolase in the retinal pigment epithelium (RPE) which converts all-trans retinyl ester (atRE) to 11-cis retinol, a key step in the visual cycle to regenerate 11cRAL. Accumulating evidence suggests that cone-dominant species express an alternative isomerase, likely in retinal Müller cells, in order to meet the high demand for the chromophore by cones. Herein we describe the identification and characterization of a novel isomerohydrolase, RPE65c, from the cone-dominant zebrafish retina. RPE65c shares 78% amino acid sequence identity with RPE-specific zebrafish RPE65a (orthologue of human RPE65) and retains all of the known key residues for the enzymatic activity of RPE65. Similar to the other RPE-specific RPE65, RPE65c was present in both the membrane and cytosolic fractions, used atRE as its substrate and required iron for its enzymatic activity. However, immunohistochemistry detected RPE65c in the inner retina including Müller cells, but not in the RPE. Furthermore, double-immunostaining of dissociated retinal cells using antibodies for RPE65c and glutamine synthetase (a Müller cell marker), showed that RPE65c co-localized with the Müller cell marker. These results suggest that RPE65c is the alternative isomerohydrolase in the intra-retinal visual cycle, providing 11cRAL to cone photoreceptors in cone-dominant species. Identification of an alternative visual cycle will contribute to the understanding of the functional differences of rod and cone photoreceptors.
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