Abstract
Formation of protein aggregates in the aging eye lens has been shown to correlate with progressive accumulation of specific low-molecular weight (LMW) peptides derived from crystallins. Prominent among the LMW fragments is αA66-80, a peptide derived from αA-crystallin and present at higher concentrations in the water-insoluble nuclear fractions of the aging lens. The αA66-80 peptide has amyloid-like properties and preferentially insolubilizes α-crystallin from soluble lens fractions. However, the specific interactions and mechanisms by which the peptide induces α-crystallin aggregation have not been delineated. To gain insight into the mechanisms of peptide-induced aggregation, we investigated the interactions of the peptide with α-crystallin by various biochemical approaches. The peptide weakens α-crystallin chaperone ability and drastically promotes α-crystallin aggregation via the formation of insoluble peptide-protein complexes through transient intermediates. 4,4'-Dianilino-1,1'-binaphthyl-5,5'-disulfonic acid studies suggest that the peptide induces changes in the hydrophobicity of α-crystallin that could trigger the formation and growth of aggregates. The peptide-α-crystallin aggregates were found to be resistant to dissociation by high ionic strengths, whereas guanidinium hydrochloride and urea were effective dissociating agents. We conclude that the αA66-80 peptide forms a hydrophobically driven, stable complex with α-crystallin and reduces its solubility. Using isotope-labeled chemical cross-linking and mass spectrometry, we show that the peptide binds to multiple sites, including the chaperone site, the C-terminal extension, and subunit interaction sites in αB-crystallin, which may explain the antichaperone property of the peptide and the consequential age-related accumulation of aggregated proteins. Thus, the α-crystallin-derived peptide could play a role in the pathogenesis of cataract formation in the aging lens.