The mechanism of the interaction of α-crystallin and UV-damaged ßL-crystallin.

α-Crystallin maintains the transparency of the lens by preventing the aggregation of damaged proteins. The aim of our work was to study the chaperone-like activity of native α-crystallin in near physiological conditions (temperature, ionic power, pH) using UV-damaged ßL-crystallin as the target protein. α-Crystallin in concentration depended manner inhibits the aggregation of UV-damaged ßL-crystallin. DSC investigation has shown that refolding of denatured UV-damaged ßL-crystallin was not observed under incubation with α-crystallin. α-Crystallin and UV-damaged ßL-crystallin form dynamic complexes with masses from 75 to several thousand kDa. The content of UV-damaged ßL-crystallin in such complexes increases with the mass of the complex. Complexes containing >10% of UV-damaged ßL-crystallin are prone to precipitation whereas those containing <10% of the target protein are relatively stable. Formation of a stable 75 kDa complex is indicative of α-crystallin dissociation. We suppose that α-crystallin dissociation is the result of an interaction of comparable amounts of the chaperone-like protein and the target protein. In the lens simultaneous damage of such amounts of protein, mainly ß and gamma-crystallins, is impossible. The authors suggest that in the lens rare molecules of the damaged protein interact with undissociated oligomers of α-crystallin, and thus preventing aggregation.

Study of α-crystallin structure by small angle neutron scattering with contrast variation.

The structure of the oligomeric protein α-crystallin from bovine eye lens was investigated by small-angle neutron scattering (SANS) with contrast variation. Based on the SANS curves, the match point for α-crystallin (43% D2O) and its average scattering length density at this point (2.4·10(10) cm(-2)) were evaluated. The radius of gyration and the distance distribution functions for α-crystallin were calculated. On the basis of these calculations, it was concluded that α-crystallin is characterized by homogeneous distribution of scattering density in the domains inaccessible for water penetration, and all polypeptide subunits in α-crystallin oligomers undergo equal deuteration. The latter indicates that all α-crystallin subunits are equally accessible for water and presumably for some other low molecular weight substances. These conclusions on the α-crystallin structure (homogeneous distribution of scattering density and equal accessibility of all subunits for low molecular weight substances) should be taken into account when elaborating α-crystallin quaternary structure models.

Resistance of alpha-crystallin quaternary structure to UV irradiation.

The damaging effect of UV radiation (lambda > 260 nm) on bovine alpha-crystallin in solution was studied by small-angle X-ray scattering, gel permeation chromatography, electrophoresis, absorption and fluorescence spectroscopy, and differential scanning calorimetry. The results obtained show that damage to even a large number of subunits within an alpha-crystallin oligomer does not cause significant rearrangement of its quaternary structure, aggregation of oligomers, or the loss of their solubility. Due to the high resistance of its quaternary structure, alpha-crystallin is able to prevent aggregation of destabilized proteins (especially of gamma- and beta-crystallins) and so to maintain lens transparency throughout the life of an animal (the chaperone-like function of alpha-crystallin).