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Heat-induced conformational change and increased chaperone activity of lens alpha-crystallin.

PURPOSE
Alpha-crystallin is the major structural protein of the eye lens known to have chaperone-like activity. Our objective is to elucidate the nature of the thermal transition that alpha-crystallin undergoes at 60 degrees C and the effect of this transition on the chaperone activity.


METHODS
FPLC size exclusion chromatography, far- and near-ultraviolet circular dichroism, and tryptophan (Trp) and 1-anilino-8-naphthalenesulfonate (ANS) fluorescence were used to study conformational change. Turbidity of dithiothreitol (DTT)-reduced insulin was used to study chaperone activity.


RESULTS
The thermal transition was identified as a conformational change in mainly tertiary (partial unfolding) and quaternary high-molecular-weight (HMW) aggregation structures, along with a loss of 10 percentage points of secondary structure (beta-sheet). Initial partial perturbation in tertiary structure increased chaperone activity, but the increase was less in the HMW aggregate. Similar results were observed in in vivo-formed HMW alpha-crystallin.


CONCLUSIONS
The conformational change and HMW aggregation of alpha-crystallin observed at 60 degrees C, as well as in vivo-formed HMW aggregates, increased chaperone activity.