RPE65

Fig1. The visual cycle in rod cells. (Ioannis Papaioannou, 2023)

What is RPE65 protein?

RPE65 (retinoid isomerohydrolase RPE65) gene is a protein coding gene which situated on the short arm of chromosome 1 at locus 1p31. The protein encoded by this gene is a component of the vitamin A visual cycle of the retina which supplies the 11-cis retinal chromophore of the photoreceptors opsin visual pigments. It is a member of the carotenoid cleavage oxygenase superfamily. All members of this superfamily are non-heme iron oxygenases with a seven-bladed propeller fold and oxidatively cleave carotenoid carbon:carbon double bonds. However, the protein encoded by this gene has acquired a divergent function that involves the concerted O-alkyl ester cleavage of its all-trans retinyl ester substrate and all-trans to 11-cis double bond isomerization of the retinyl moiety. As such, it performs the essential enzymatic isomerization step in the synthesis of 11-cis retinal. The RPE65 protein is consisted of 533 amino acids and its molecular mass is approximately 60.9 kDa.

What is the function of RPE65 protein?

The RPE65 protein is an enzyme located in retinal pigment epithelial cells (RPE) that is responsible for catalyzing the isomerization process of retinol (vitamin A). In the visual cycle, the RPE65 protein converts all-trans retinol to 11-cis-retinol, a step that is essential for the regeneration of rhodopsin in photoreceptor cells. The RPE65 protein helps regenerate rhodopsin in photoreceptor cells by participating in the metabolism of retinol, thereby maintaining normal light sensing function. The RPE65 protein also has antioxidant properties that protect the retina from oxidative stress. The RPE65 protein helps maintain the structure and function of photoreceptor cells by participating in the visual cycle and antioxidant processes, thus ensuring the normal transmission of visual signals.

RPE65 Related Signaling Pathway

The RPE65 protein plays a key role in the visual cycle. The visual cycle is a series of biochemical reactions used to regenerate rhodopsin, a photoreceptor protein in the eye. When light enters the eye, rhodopsin is broken down into all-trans retinal and opsin. The RPE65 protein converts retinal into 11-cis retinal, a form necessary for rhodopsin regeneration. The RPE65 protein is also involved in the metabolic process of vitamin A and may help maintain the healthy state of the retina by regulating vitamin A metabolism.

RPE65 Related Diseases

Retinitis Pigmentosa (RP): This is a group of hereditary eye diseases that mainly affect the rods and cones in the retina, causing symptoms such as night blindness, reduced field of vision, and diminished vision. RPE65 mutation is one of the main causes of RP. Some RPE65 mutations may lead to visual dysplasia, such as retinal hypoplasia and retinal detachment. Some drugs may affect the function of the RPE65 protein, leading to retinal damage and vision loss.

Bioapplications of RPE65

Although there are currently no commercially available RPE65 protein replacement therapies, it is theoretically possible that a therapeutic strategy could be developed by directly supplementing RPE65 protein or its active form. With gene therapy, the normal RPE65 gene can be delivered into the affected retinal cells to restore the normal function of the RPE65 protein. For example, the U.S. Food and Drug Administration (FDA) approved Luxturna (voretigene neparvovec-rzyl) is a gene therapy drug based on an AAV virus vector for the treatment of a specific type of RPE65-associated LCA.

Case Study 1: Marco Bassetto, 2023

In the eye, the isomerization of all-trans-retinal to 11-cis-retinal is accomplished by a metabolic pathway termed the visual cycle that is critical for vision. RPE65 is the essential trans-cis isomerase of this pathway. Emixustat, a retinoid-mimetic RPE65 inhibitor, was developed as a therapeutic visual cycle modulator and used for the treatment of retinopathies. However, pharmacokinetic liabilities limit its further development including: (1) metabolic deamination of the γ-amino-α-aryl alcohol, which mediates targeted RPE65 inhibition, and (2) unwanted long-lasting RPE65 inhibition. The researchers sought to address these issues by more broadly defining the structure-activity relationships of the RPE65 recognition motif via the synthesis of a family of novel derivatives, which were tested in vitro and in vivo for RPE65 inhibition. They identified a potent secondary amine derivative with resistance to deamination and preserved RPE65 inhibitory activity.

Fig1. Chemical structures and corresponding dose–response curves of γ-amino-α-aryl alcohols.

Fig2. Illustration of RPE65 residues within 4.5 Å from the bound ligands.

Case Study 2: Ya-Chih Huang, 2023

Diabetic retinopathy (DR) is a common complication of diabetes that causes visual impairment and blindness in adults. This study aimed to explore the protective effects of n-Butylidenephthalide (BP) on hyperglycemia-treated RPE in vitro and in vivo. C57BL/6 mice were injected with STZ by intraperitoneal to induce early DR and orally administrated with 2 mg/kg BP every day for twelve weeks. The outer blood-retinal barrier integrity and RPE65 expression of retina were evaluated by immunofluorescence. In in vitro study, ARPE-19 cells were long-term cultured with high glucose and BP for 8 days and studied for cell survival, tight junction integrity, RPE65 expression, angiogenic factors, mitochondria membrane potential (MMP), and ROS by MTT assay, Western blot, β-galactosidase staining, immunofluorescence, JC-1, or DCFH-DA. The results indicate that BP suppressed the hyperglycemic effect and maintained retina anatomy normalization, as well as protected RPE cell survival, tight junction integrity, and RPE65 expression in vitro and in vivo.

Fig3. BP ameliorated tight junction impairment and retinoid isomerase loss of RPE layer in hyperglycemia.

Fig4. BP promoted tight junction, retinoid regeneration, and anti-angiogenesis capacity on high glucose-treated ARPE-19 cells.

RPE65 has several biochemical functions, for example, all-trans-retinyl-ester hydrolase, 11-cis retinol forming activity,all-trans-retinyl-palmitate hydrolase, 11-cis retinol forming activity,cardiolipin binding. Some of the functions are cooperated with other proteins, some of the functions could acted by RPE65 itself. We selected most functions RPE65 had, and list some proteins which have the same functions with RPE65. You can find most of the proteins on our site.

RPE65 has direct interactions with proteins and molecules. Those interactions were detected by several methods such as yeast two hybrid, co-IP, pull-down and so on. We selected proteins and molecules interacted with RPE65 here. Most of them are supplied by our site. Hope this information will be useful for your research of RPE65.