The effects of sonication on alpha-crystallin.

Sonication of bovine alpha-crystallin increases its molecular mass from around 770 kDa to in excess of 2,300 kDa. Exposure to 2M urea or 0.1 M glycine pH 7, did not affect the size of the sonicated protein, indicating that it did not consist of dimers and higher polymers of the original molecule. Sonication of a mixture of alpha-crystallins labelled on the A chain sulphydryl group with either an aminonaphthalene or a fluorescein chromophore, generated a product exhibiting substantial energy transfer. The average distance between the probes was calculated to be 5 nm. These observations suggest that sonication has generated a new quaternary structure, incorporating subunits from two or more different alpha-crystallin molecules. No significant differences were observed in the microenvironments of tryptophan residues although those in the sonicated protein could be more easily exposed by controlled denaturation with urea. A small decrease was observed in the quenchability of a fluorescent probe attached to the sulphydryl group and a small increase in the uptake of an hydrophobic probe. These data suggest that sonication may have altered the conformation of the subunits at, or near the surface of the protein.