The effect of temperature on the renaturation of alpha-crystallin

The effects of variations in temperature and protein concentration on the renaturation of bovine alpha-crystallin have been examined using gel permeation chromatography, sedimentation analysis, fluorescence spectroscopy and electron microscopy. High protein concentration (3-53 mg/ml) were found to generate heterogenous populations of aggregates. It was concluded that concentrations above 3 mg/ml were inappropriate for renaturation of alpha-crystallin. Aggregates with molecular masses gradually increasing from 461,000 to 695,000 Da were produced with increasing temperature over the range 6-39 degrees C. Electron microscopy demonstrated that the reaggregates were composed predominantly of particles with circular cross-sections and mean diameters of 13-14 nm. As the renaturation temperature increased, increasing amounts of sheet-like structures were observed. Tryptophan accessibility to acrylamide quenching decreased in these aggregates as the size increased. These observations are consistent with the concept that there is no unique quaternary structure, or set of structures, for alpha-crystallin but that the protein can exist in a variety of forms containing different numbers of subunits.