Abstract
alpha-Crystallin, a multimeric protein, exhibits chaperone-like activity in preventing aggregation of several proteins. We have studied the chaperone-like activity of alpha-crystallin toward heat-induced aggregation of bovine and human carbonic anhydrase. Human carbonic anhydrase aggregates at 60 degrees C, while bovine carbonic anhydrase does not aggregate significantly at this temperature. Removal of the enzyme-bound metal ion, Zn2+, by EDTA modulates the aggregation behavior of bovine carbonic anhydrase. Fluorescence and circular dichroism studies show that removal of the metal ion from the bovine carbonic anhydrase by a chelator such as EDTA enhances the propensity of the enzyme to adopt the molten-globule state. alpha-Crystallin binds to this state of the enzyme and prevents aggregation. Fluorescence and circular dichroism studies on the alpha-crystallin-enzyme complexes show that the enzymes in the complex are in the molten-globule state. These results are of relevance to the interaction of chaperones with the partially unfolded states of target proteins.
Highlights
␣-Crystallin from the old human lenses [24] and from the selenite-induced cataractous lenses of an animal model [25] are found to exhibit decreased chaperone-like activity
We have observed that human carbonic anhydrase aggregates at 60 °C while the aggregation of bovine carbonic anhydrase is negligible at the same temperature
␣-Crystallin is known to prevent the aggregation of other proteins
Summary
␣-Crystallin from the old human lenses [24] and from the selenite-induced cataractous lenses of an animal model [25] are found to exhibit decreased chaperone-like activity. The results suggest that ␣-crystallin binds to the molten-globule states of these proteins and prevents their aggregation.
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