Lens Oligomerization with wt a Aand a B-Crystallins Reduces Proteasome-Mediated Degradation of C-Terminally Truncated a A-Crystallin

PURPOSE. We previously demonstrated that the ubiquitinproteasome pathway (UPP) is a general protein quality control system that selectively degrades damaged or abnormal lens proteins, including C-terminally truncated aA-crystallin. The objective of this work was to determine the effects of wt aAand aB-crystallins on the degradation of C-terminally truncated aA-crystallin (aA1–162) and vice versa. METHODS. Recombinant wt aA, aB, and aA1–162 were expressed in Escherichia coli and purified to homogeneity by chromatography. Subunit exchange and oligomerization were detected by fluorescence resonance energy transfer (FRET), multianglelight scattering and coprecipitation assays. Protein substrates were labeled with I and lens epithelial cell lysates were used as the source of the UPP for degradation assays.