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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #37767
Title: DEGRADATION OF DIFFERENTIALLY OXIDIZED ALPHA-CRYSTALLIN IN BOVINE LENS EPITHELIAL CELLS

Author
item HUANG LI LI - TUFTS-HNRCA
item SHANG FU - TUFTS-HNRCA
item TAYLOR ALLEN - TUFTS-HNRCA

Submitted to: Experimental Eye Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: As the lens ages, it becomes opaque. The opacity is called cataract. Most aged persons develop cataract. It is thought that the cataract is due to accumulation of damaged or oxidized protein. It is also thought that in younger cells, damaged proteins are more readily degraded. In this paper, we examine which degradation systems are available in the lens, and we examine how they work on damaged proteins.

Technical Abstract: There is a growing consensus that altered proteins are more susceptible to degradation than native proteins. The enhancement of degradation of damaged proteins may be of significance since it prevents the accumulation of damaged proteins in the cells. Several proteolytic pathways have been discovered in the lens, but the extent of involvement of these proteolytic pathways in degradation of damaged proteins is not well described. Alpha- crystallin was oxidized by exposure to 0.03-3.2 mol .OH/mol protein. Modifications to the oxidized alpha-crystallin and proteolytic susceptibility of the oxidized alpha-crystallin were studied. Exposure to >0.32 mol .OH/mol subunit produced aggregates and fragments of alpha- crystallin. Changes in isoelectric points of the proteins were observed after exposure to 0.64 mol .OH/mol protein. The level of exposure was also associated with loss of tryptophan and sulfhydryl groups, and in- crease in carbonyl content. When incubated with a supernatant of bovine lens epithelial cells, the .OH-modified proteins were proteolytically degraded up to 3 times faster than untreated alpha-crystallin. ATP stimulated the degradation of native alpha-crystallin and alpha-cry- stallin which was exposed to 1.6 mol .OH/mol subunit protein (alpha1.6). Sixty eight percent and 100% of the ATP-dependent degradation of native alpha-crystallin and alpha1.6 was ubiquitin-dependent, respectively. The data indicate that alpha-crystallin oxidized by .OH are recognized and degraded rapidly by cytoplasmic proteolytic systems in bovine lens epithelial cells. Both ATP-independent and ATP/ubiquitin-dependent proteolytic pathways are involved in the degradation of native and oxidized alpha-crystallin.