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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1995 Feb 14;92(4):1067–1071. doi: 10.1073/pnas.92.4.1067

Oxidation of gamma II-crystallin solutions yields dimers with a high phase separation temperature.

J Pande 1, A Lomakin 1, B Fine 1, O Ogun 1, I Sokolinski 1, G Benedek 1
PMCID: PMC42638  PMID: 7862635

Abstract

Aqueous solutions of the bovine eye lens protein gamma II (or gamma B)-crystallin at neutral pH show a gradual increase in phase separation temperature, Tph, when allowed to stand for several weeks at room temperature without reducing agents. In a typical experiment, the Tph of the protein solution (218 mg/ml) increases from 2.5 +/- 1 degree C to 32.5 +/- 1 degree C after 21 days, and a new protein species, gamma IIH, is formed. The Tph of pure gamma IIH is at least 40 degrees C higher than that of pure gamma II. The average apparent hydrodynamic radius is 36 A for gamma IIH compared to 26 A for gamma II. The molecular mass of gamma IIH is approximately 41.5 kDa compared to 20 kDa for native gamma II. Therefore, gamma IIH is probably a dimer of gamma II crystallin. gamma IIH has a lower thiol content than gamma II and is not formed in the presence of dithiothreitol. We conclude that gamma IIH is a thiol oxidation product of gamma II-crystallin and is a dimer containing an intermolecular disulfide crosslink. Thus, some oxidative modifications of protein thiol groups lead to an increase in net attractive interactions between proteins. As a result, Tph increases and protein aggregates are formed. These two microscopic changes produce the increased light scattering associated with lens opacification.

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Selected References

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