Deamidation of the human eye lens protein γS-crystallin accelerates oxidative aging

• Published in: Structure (London) Vol. 30; no. 5; pp. 763 - 776.e4
• Main Authors: Norton-Baker, Brenna, Mehrabi, Pedram, Kwok, Ashley O., Roskamp, Kyle W., Rocha, Megan A., Sprague-Piercy, Marc A., von Stetten, David, Miller, R.J. Dwayne, Martin, Rachel W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 05.05.2022; Elsevier
• Subjects: BASIC BIOLOGICAL SCIENCES; cataract; Cataract - genetics; Cataract - metabolism; crystallin; deamidation; disulfide bonding; gamma-Crystallins - chemistry; gamma-Crystallins - genetics; Humans; Lens, Crystalline - chemistry; Lens, Crystalline - metabolism; oxidation; Oxidation-Reduction; Oxidative Stress; post-translational modification; protein aggregation; protein stability; second virial coefficient; X-ray crystallography; deamidation; X-ray crystallography; second virial coefficient; cataract; protein aggregation; oxidation; post-translational modification; crystallin; protein stability; disulfide bonding
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2022.03.002

Cataract, a clouding of the eye lens from protein precipitation, affects millions of people every year. The lens proteins, the crystallins, show extensive post-translational modifications (PTMs) in cataractous lenses. The most common PTMs, deamidation and oxidation, promote crystallin aggregation; however, it is not clear precisely how these PTMs contribute to crystallin insolubilization. Here, we report six crystal structures of the lens protein γS-crystallin (γS): one of the wild-type and five of deamidated γS variants, from three to nine deamidation sites, after sample aging. The deamidation mutations do not change the overall fold of γS; however, increasing deamidation leads to accelerated disulfide-bond formation. Addition of deamidated sites progressively destabilized protein structure, and the deamidated variants display an increased propensity for aggregation. These results suggest that the deamidated variants are useful as models for accelerated aging; the structural changes observed provide support for redox activity of γS-crystallin in the lens. [Display omitted] •Crystal structures of cataract-associated variants of γS-crystallin reported•Increasing deamidation decreases stability and affects aggregation propensity•Overall fold of γS maintained among deamidated and disulfide-bonded variants•Deamidated γS variants form disulfide bonds more rapidly than wild-type γS To mimic the accumulation of deleterious post-translational modifications in the eye lens, Norton-Baker et al. investigate a series of cataract-related variants of the lens protein γS-crystallin with progressively more deamidation sites. Increased disulfide bonding and aggregation suggest that both surface charge and increased dynamics impact cataract formation by deamidated crystallins.