Detection of structural changes of alpha‐crystallin upon binding of metals.

Abstract

Alpha-crystallin, one of the most abundant proteins in the lens is known to be a member of the heat shock family and a molecular chaperone. This protein prevents the aggregation of other lens proteins which can occur under stressful conditions and may be a factor in cataractogenesis, a clouding of the lens. Also, α-crystallin has been shown to assist in the in vitro folding of other polypeptides. Many molecular chaperones require cofactors and none has been clearly identified for α-crystallin. We used the detection of conformational changes of α-crystallin upon incubation with several metals as a means for the identification of possible cofactors for this protein. Interestingly, we found that calcium significantly altered the conformation of α-crystallin as detected with tryptophan fluorescence spectroscopy. Furthermore, studies using the fluorescent probe, bisANS, indicated that these structural changes led to an increased exposure of hydrophobic surfaces on α-crystallin. Finally, as the concentration of the metal was increased to levels such as those found in cataracts, the protein was shown to aggregate as monitored by light scattering as well as thioflavinT spectroscopy.