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首页> 外文期刊>The FEBS journal >An alternative isomerohydrolase in the retinal Muller cells of a cone-dominant species
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An alternative isomerohydrolase in the retinal Muller cells of a cone-dominant species

机译：视锥细胞优势种的视网膜穆勒细胞中的另一种异构水解酶

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摘要

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) that converts all-trans retinyl ester to 11-cis retinol, a key step in the visual cycle for regenerating 11cRAL. Accumulating evidence suggests that cone-dominant species express an alternative isomerase, likely in retinal Muller cells, to meet the high demand for the chromophore by cones. In the present study, 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 all-trans retinyl ester as its substrate and required iron for its enzymatic activity. However, immunohistochemistry detected RPE65c in the inner retina, including Muller cells, but not in the RPE. Furthermore, double-immunostaining of dissociated retinal cells using antibodies for RPE65c and glutamine synthetase (a Muller cell marker), showed that RPE65c co-localized with the Muller 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.
机译：圆锥形感光体比棒状感光体具有更快的光响应，并且对11-顺式视网膜（11cRAL）（可视色素的发色团）的需求更高。 RPE65是视网膜色素上皮（RPE）中的异构水解酶，可将全反式视黄酯转变为11-顺式视黄醇，这是再生11cRAL的视觉循环的关键步骤。越来越多的证据表明，视锥细胞占主导地位的物种可能在视网膜穆勒细胞中表达一种替代异构酶，以满足视锥细胞对发色团的高需求。在本研究中，我们描述了一种来自圆锥占主导地位的斑马鱼视网膜的新型异构水解酶RPE65c的鉴定和表征。 RPE65c与RPE特异性斑马鱼RPE65a（人类RPE65的同源物）共有78％的氨基酸序列同一性，并保留了RPE65酶促活性的所有已知关键残基。与其他RPE特异的RPE65相似，RPE65c既存在于膜级分又存在于胞质级分中，使用全反式视黄酯作为底物，并需要铁来发挥其酶促活性。但是，免疫组织化学检测到包括穆勒细胞在内的视网膜内部存在RPE65c，但在RPE中未检测到。此外，使用RPE65c和谷氨酰胺合成酶（穆勒细胞标记）的抗体对分离的视网膜细胞进行双重免疫染色，显示RPE65c与穆勒细胞标记共定位。这些结果表明，RPE65c是视网膜内视觉周期中的替代异构水解酶，为视锥细胞占主导地位的视锥细胞提供11cRAL。确定替代的视觉周期将有助于理解杆和锥光感受器的功能差异。

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