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Dynamic disulfide exchange in a crystallin protein in the human eye lens promotes cataract-associated aggregation.


ABSTRACT: Increased light scattering in the eye lens due to aggregation of the long-lived lens proteins, crystallins, is the cause of cataract disease. Several mutations in the gene encoding human ?D-crystallin (H?D) cause misfolding and aggregation. Cataract-associated substitutions at Trp42 cause the protein to aggregate in vitro from a partially unfolded intermediate locked by an internal disulfide bridge, and proteomic evidence suggests a similar aggregation precursor is involved in age-onset cataract. Surprisingly, WT H?D can promote aggregation of the W42Q variant while itself remaining soluble. Here, a search for a biochemical mechanism for this interaction has revealed a previously unknown oxidoreductase activity in H?D. Using in vitro oxidation, mutational analysis, cysteine labeling, and MS, we have assigned this activity to a redox-active internal disulfide bond that is dynamically exchanged among H?D molecules. The W42Q variant acts as a disulfide sink, reducing oxidized WT and forming a distinct internal disulfide that kinetically traps the aggregation-prone intermediate. Our findings suggest a redox "hot potato" competition among WT and mutant or modified polypeptides wherein variants with the lowest kinetic stability are trapped in aggregation-prone intermediate states upon accepting disulfides from more stable variants. Such reactions may occur in other long-lived proteins that function in oxidizing environments. In these cases, aggregation may be forestalled by inhibiting disulfide flow toward mutant or damaged polypeptides.

SUBMITTER: Serebryany E 

PROVIDER: S-EPMC6240864 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Dynamic disulfide exchange in a crystallin protein in the human eye lens promotes cataract-associated aggregation.

Serebryany Eugene E   Yu Shuhuai S   Trauger Sunia A SA   Budnik Bogdan B   Shakhnovich Eugene I EI  

The Journal of biological chemistry 20180921 46


Increased light scattering in the eye lens due to aggregation of the long-lived lens proteins, crystallins, is the cause of cataract disease. Several mutations in the gene encoding human γD-crystallin (HγD) cause misfolding and aggregation. Cataract-associated substitutions at Trp<sup>42</sup> cause the protein to aggregate <i>in vitro</i> from a partially unfolded intermediate locked by an internal disulfide bridge, and proteomic evidence suggests a similar aggregation precursor is involved in  ...[more]

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