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FUNCTIONAL PROTEOMICS
OF THE EYE: UNDERSTANDING THE VISUAL CYCLE AND APPLICATION TOWARD THE TREATMENT
OF EYE DISEASES
The absorption of light by
rhodopsin causes photoisomerization of 11-cis-retinal Schiff base
chromophore into all-trans isomer. Nature has chosen two recycling
pathways-rhodopsin cycle and retinoid cycle- for continued vision. 11-cis-retinal
must be regenerated in the eye where only 11-cis retinoid are found in
the body. This retinoid cycle, also called visual cycle, is mediated by the
series of the membrane proteins in the retinal pigment epithelial (RPE) cells.
Carefully designed affinity labeling reagents reveal the identity and the role
of essential proteins in the RPE. One of the key enzymes, lecithin retinol
acyltransferase (LRAT), catalyzes esterification of the vitamin A. LRAT is a
founder member of a novel family of enzymes showing the unusual catalytic triad.
A biotin containing vitamin A analog is also sought to facilitate
characterization of retinoid binding proteins in the RPE. Indeed, alkali
cleavable affinity biotinylating agent demonstrates that RPE65, a major
membrane-associated protein in the RPE, is a retinyl ester binding protein. By
using functional proteomic tools such as chemical crosslinkers, non-reducing SDS-PAGE,
2D-SDS-PAGE and mass spectrometric analysis, functional LRAT homodimer
formation, protein-protein interaction, visual cycle protein complex formation
were uncovered. Understanding specific protein-protein interaction and function,
complex formation, palmitoylation of some essential proteins for vision reveal
the visual cycle mechanism on the molecular level. The biochemical mechanistic
study has application to treat certain eye disease such as age-related macular
degeneration. Also, other functional proteomics project including
cytomegalovirus protein function, insulin action and regulation, drug
design/synthesis/evaluation, developing bioinformatic tool to predict certain
protein-protein interactions is under the study.
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