The Role of Chaperone Proteins in Cataract Aggregation: A Two-Dimensional Infrared Study

Abstract

Crystallin proteins need to maintain their native structures at high concentration in the lens to enable vision. When these proteins aggregate into opaque deposits, cataracts are formed. Most kinds of isolated crystallin proteins form amyloid fibril structures when treated with denaturants in vitro, but these structures have not been confirmed from examination of a cataractous lens. It is hypothesized that alpha crystallins form molecular chaperones that bind to unfolded proteins and interrupt the aggregation pathways. We study the aggregation of gammaD-crystallin in the presence of alphaB-crystallin with two-dimensional infrared (2D IR) spectroscopy that is sensitive to the secondary structure of proteins. Using 13C isotope labeling of either the gammaD-crystallin or the alphaB-crystallin, we can independently watch structural changes in both proteins simultaneously. In addition, cross-peaks in the 2D IR spectra reveal coupling between the different proteins. Using these tools, we have observed interaction between alphaB-Crystallin and aggregated gammD-Crystallin. Our study provides a new way of monitoring protein-protein interactions and will be valuable in the further studies of molecular chaperone interactions with disease-related protein aggregates and their intermediates.