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UNCTIONAL
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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