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. 1997 Sep 19;272(38):23559-64.
doi: 10.1074/jbc.272.38.23559.

Chaperone-like activity and temperature-induced structural changes of alpha-crystallin

B Raman  1 , C M Rao
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Free article

Chaperone-like activity and temperature-induced structural changes of alpha-crystallin

B Raman et al. J Biol Chem. .
Free article

Abstract

alpha-Crystallin is known to exhibit chaperone-like activity. We have studied its chaperone-like activity toward the aggregation of betaL-crystallin upon refolding of this protein from its unfolded state in guanidinium chloride. The chaperone-like activity of alpha-crystallin is less pronounced below 30 degrees C and is enhanced above this temperature. The plot of percentage protection as a function of temperature shows two transitions; one at 30 degrees C and another at around 55 degrees C. We have performed steady state fluorescence, fluorescence polarization, fluorescence quenching, circular dichroism, sedimentation analysis, and gel filtration chromatography to probe the temperature-induced structural changes of alpha-crystallin. Our results show that at above 50 degrees C, alpha-crystallin undergoes a transition to a multimeric molten globule-like state. Above 30 degrees C, a minor but detectable perturbation in its tertiary structure occurs that might lead to the observed exposure of its hydrophobic surfaces. These results support our earlier hypothesis that alpha-crystallin prevents the aggregation of other proteins by providing appropriately placed hydrophobic surfaces; a structural transition above 30 degrees C involving enhanced or reorganized hydrophobic surfaces of alpha-crystallin is important for its chaperone-like activity. It is possible that a structural alteration induced by temperature forms a part of the general mechanism of chaperone function, because they are required to function more effectively at nonpermissible temperatures.

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