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This Sandbox is Reserved from Jan 13 through July 31, 2020 for use in the course Protein Structure in Drug Discovery taught by Karen C. Glass at the ACPHS, Colchester, United States. This reservation includes Sandbox Reserved 895 through Sandbox Reserved 901.

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1. Introduction

In humans the vertebrate vision is maintained by a chemical process known as the retinoid (visual) cycle. This cycle is a complex enzymatic pathway that operates within the retina to regenerate a key visual chromophore known as 11-cis-retinal. The enzyme responsible for regenerating the key visual chromophore, 11-cis-retinal is a microsomal membrane protein retinal pigment epithelium 65 also known as RPE65. The RPE65 enzyme catalyzes the chemical conversion of all-trans-retinyl ester (or all-trans-retinyl palmityl ester) to 11-cis-retinol within the human retinal pigment epithelium (hRPE). ^[1]

RPE65 is located within the hRPE cells located in the back of the eye. The human retinal pigment epithelium is responsible for regulating the nourishment of the retina. Since the retinoid (visual) cycle requires the incorporation of light into catalyzing chemical reactions, hRPE cells are light sensitive.

The Retinoid (Visual) Cycle

For humans to see, the retinoid (visual) cycle converts incident light entering into the eye to electrochemical signals that can be transmitted to the brain as neuronal impulses. The chemical reactions that take place within the retinoid cycle allows the regeneration of key intermediates to allow for vision to take place. Dysregulation of these chemical processes, associated with disease, can lead to alterations in vision and blindness. Age related macular degeneration is an example of the dysregulation within the retinoid cycle. The 3-dimensional binding site of bovine RPE65 to an exogenous substrate (R)-emixustat shown in Figure 1, was a tested drug treatment for dry age related macular degeneration.

References

1. ↑ Kiser PD, Golczak M, Lodowski DT, Chance MR, Palczewski K. Crystal structure of native RPE65, the retinoid isomerase of the visual cycle. Proc Natl Acad Sci U S A. 2009 Oct 13;106(41):17325-30. Epub 2009 Oct 5. PMID:19805034