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.
Putilina
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Russell Grimwade School of Biochemistry, University of Melbourne, Parkville, Victoria, Australia.
Zhang
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ZW
Augusteyn
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RC
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003459:Crystallins / Q000737:chemistry*; D007908:Lens, Crystalline / Q000000981:diagnostic imaging; D008970:Molecular Weight; D011487:Protein Conformation; D013010:Sonication; D013050:Spectrometry, Fluorescence; D014463:Ultrasonography
D003459:Crystallins