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I. A. Mills, S. L. Thol, J. A. King; Differential Kinetic Stability of Gamma D and Gamma S Lens Crystallins, and Their Isolated Double Greek Key Domains. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4089. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The transparency of the human eye lens depends on the properties of the α-crystallin and βγ-crystallin proteins, which accumulate to very high concentrations in lens fiber cells. Terminally differentiated fiber cells are enucleated and devoid of all other organelles, and are unable to degrade damaged crystallins or synthesize new ones. Thus, the crystallins must remain soluble for decades despite high concentrations of protein, continual UV exposure and potential oxidative stress. The biochemical basis for crystallin stability is of considerable importance in understanding the etiology of the loss of lens transparency leading to cataract formation. The kinetic stability of two homologous yet divergent crystallins, HγD crystallin (HγD-Crys) and HγS crystallin (HγS-Crys), and their respective isolated domains was determined and compared. HγD-Crys is synthesized in utero and must remain stable and soluble throughout life. Comparatively, HγS-Crys is more prevalent in the outer cortex of the lens, where predictably protein degradation and synthesis still occurs.
Kinetic unfolding of the all crystallins was performed in different concentrations of GuHCl, monitored by fluorescence spectroscopy. The kinetic rates and half-lives of the crystallins were calculated for each condition.
The unfolded kinetic rates and half-lives for the crystalllins at different GuHCl conditions were extrapolated to the absence of denaturant. The calculated t1/2 for the initial unfolding step of HγD-Crys was ~19 years. The half-life extrapolated for HγS-Crys was not as long, though still significant. All of the unfolded kinetic half-lives of the isolated domain crystallins were less than their respective full-length proteins.
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