June 2021
Volume 62, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2021
Retinylation of Opsins by Retinyl Formate
Author Affiliations & Notes
  • John Hong
    Ophthalmology, University of California Irvine School of Medicine, Irvine, California, United States
  • Ángel Placeres
    Chemistry, Case Western Reserve University, Cleveland, Ohio, United States
  • Gregory P Tochtrop
    Chemistry, Case Western Reserve University, Cleveland, Ohio, United States
  • Footnotes
    Commercial Relationships   John Hong, None; Ángel Placeres, None; Gregory Tochtrop, None
  • Footnotes
    Support  5T32GM008620-22; 5R01EY009339-31
Investigative Ophthalmology & Visual Science June 2021, Vol.62, 2992. doi:
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      John Hong, Ángel Placeres, Gregory P Tochtrop; Retinylation of Opsins by Retinyl Formate. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2992.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Defects in visual cycle enzymes or retinoid carrier proteins may deplete 11-cis retinal (11cRAL) and are implicated in multiple blinding diseases. Therefore, retinal analogues that aid in vision independent of chromophore recycling have invaluable translational implications in addressing visual cycle impairments and controlling visual cycle kinetics. Conversely, intense light exposure causing overstimulation of photoreceptors can overwhelm the outer segment with atRAL that form toxic bisretinoid lipofuscin species that contribute to Age-Related Macular Degeneration. Therefore, retinal analogues also have an important role in either attenuating opsin activity or serving as transient molecular brakes of the visual cycle.

Methods : The chemistry of retinyl formate (RF) in forming a covalent interaction with primary amines of lysine was tested in solution with different solvent, and the resultant reaction mixture was analyzed by high performane liquid chromatography. The covalent binding efficiency of RF was assessed by UV-Vis spectrophotometry. The site of retinyl modification by RF was determined by protein digest of RF treated opsin, followed by peptide liquid chromatography mass spectrometry (LC-MS).

Results : RF interacts with primary amines to form a covalent interaction, producing a retinyl secondary amine. The UV-Vis spectrum of the RF treated opsin that was thoroughly washed shows a spectrum resembling opsin modified by a retinyl group. Over time, the spectrum gradually shifted to that of the Schiff base, demonstrating that the modification is transient and reverts to normal opsin physiology. Protein digest of our positive control in borohydride reduced native bovine rhodopsin and subsequent peptide LC-MS showed presence of retinyl peptides. The same will be done on RF treated rhodopsin.

Conclusions : RF can serve as retinylating agent of amines and therefore likely retinylates the amine side chain of lysine within the chromophore binding pocket of opsin. RF treated opsin shows spectrum indicative of such a reaction occuring within opsin. Retinylated opsin gradually oxidized to the Schiff base, suggesting that the modification can be a way to restore visual pigment. Protein digest and peptide LC-MS on borohydride reduce native bovine rhodopsin demonstrated efficacy in detecting retinyl peptides; therefore, the same can be done on retinylated opsin to confirm the retinylation modification and the preference site of modification within opsin.

This is a 2021 ARVO Annual Meeting abstract.

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