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  • Title: Oligomerization with wt αA- and αB-crystallins reduces proteasome-mediated degradation of C-terminally truncated αA-crystallin.
    Author: Wu M, Zhang X, Bian Q, Taylor A, Liang JJ, Ding L, Horwitz J, Shang F.
    Journal: Invest Ophthalmol Vis Sci; 2012 May 04; 53(6):2541-50. PubMed ID: 22427585.
    Abstract:
    PURPOSE: We previously demonstrated that the ubiquitin-proteasome pathway (UPP) is a general protein quality control system that selectively degrades damaged or abnormal lens proteins, including C-terminally truncated αA-crystallin. The objective of this work was to determine the effects of wt αA- and αB-crystallins on the degradation of C-terminally truncated αA-crystallin (αA(1-162)) and vice versa. METHODS: Recombinant wt αA, αB, and αA(1-162) were expressed in Escherichia coli and purified to homogeneity by chromatography. Subunit exchange and oligomerization were detected by fluorescence resonance energy transfer (FRET), multiangle-light scattering and coprecipitation assays. Protein substrates were labeled with (125)I and lens epithelial cell lysates were used as the source of the UPP for degradation assays. RESULTS: FRET, multiangle light scattering, and coprecipitation assays showed that αA(1-162) exchanged subunits with wt αA- or wt αB- crystallin to form hetero-oligomers. αA(1-162) was more susceptible than wt αA-crystallin to degradation by the UPP. When mixed with wt αA-crystallin at 1:1 or 1:4 (αA(1-162) : wt) ratios to form hetero-oligomers, the degradation of αA(1-162) was significantly decreased. Conversely, formation of hetero-oligomers with αA(1-162) enhanced the degradation of wt αA-crystallin. The presence of αA(1-162), but not wt αA-crystallin, decreased the degradation of wt αB-crystallin. CONCLUSIONS: αA(1-162) forms hetero-oligomers with wt αA- and αB-crystallins. Oligomerization with wt αA- or αB-crystallins reduces the susceptibility of αA(1-162) to degradation by the UPP. In addition, the presence of αA(1-162) in the hetero-oligomers also affects the degradation of wt αA- and αB-crystallins.
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