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Rooban B Nahomi, Ram H Nagaraj; Acylation of αB-Crystallin in Human Lens and Retina. Invest. Ophthalmol. Vis. Sci. 2016;57(12):723.
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© ARVO (1962-2015); The Authors (2016-present)
αB-Crystallin (HSPB5) is a molecular chaperone and an anti-apoptotic protein. It is a major protein in vertebrate lenses but also present in significant amounts in other tissues, including retina. We previously found that lysine residues in αB-crystallin in human lens are acetylated, which alters its structure and function. Here we investigated succinylation of αB-crystallin in normal lenses of varying age, cataractous lenses, and human non-diabetic and diabetic retinas and the effect of succinylation on αB-crystallin’s function.
Water soluble and insoluble fractions were prepared from human lenses of varying age (9 to 86 years) and cataracts. LC-MS/MS was used to identify succinylated lysine residues in human lens αB-crystallin. In vitro succinylated αB-crystallin was tested in chaperone assays for changes in activity. Succinylation and acetylation of retinal proteins, in particular αB-crystallin, was investigated in the retinas from non-diabetic and diabetic donors by western blotting.
Western blotting experiments indicated that αB-crystallin was succinylated in human lenses, which was confirmed in immunoprecipitation experiments. There was no change in the extent of succinylation of αB-crystallin in normal aging lenses. We identified succinylation of K150 in αB-crystallin from a 33-year old donor lens. In vitro succinylation of αB-crystallin was achieved by reacting the protein with succinic anhydride and confirmed by western blotting and mass spectrometry. The chaperone activity of αB-crystallin increased after succinylation and it was dependent on the extent of succinylation. We detected succinylated lysine residues in a number of retinal proteins, but it was more apparent in αB-crystallin. Immunoprecipitation experiments confirmed acylation of αB-crystallin in human retinas. Remarkably, diabetic retinas showed higher levels of both acetyllysine and succinyllysine-bearing proteins than non-diabetic retinas.
Acylation of αB-crystallin occurs in human lens and retina and this modification enhances its chaperone activity. Acylation is not age-dependent in human lenses. However, acylation of retinal proteins, especially αB-crystallin is increased in diabetes. Acylation of lysine residues could be important posttranslational modifications in αB-crystallin to enhance its activity to protect tissues against metabolic and environmental stresses.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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