X-ray- and neutron-scattering studies of alpha-crystallin and evidence that the target protein sits in the fenestrations of the alpha-crystallin shell.
ABSTRACT Alpha-crystallin, a ubiquitous molecular chaperone, is found in high concentrations in the lens. Its structure and precise mechanism of action, however, are unknown. The purpose of these experiments was to further the understanding of the chaperone function of alpha-crystallin.
X-ray- and neutron-solution-scattering studies were used to measure the radius of gyration of bovine lens alpha-crystallin when complexed with its target protein beta-crystallin in both normal and heavy-water-based solutions. Spectrophotometry was used as a chaperone assay.
The radius of gyration of alpha-crystallin on its own and when mixed with beta-crystallin was 69 +/- 1 A at 35 degrees C and increased with the temperature. In contrast to H2O-buffered solutions, the radius of gyration did not increase significantly in D2O-buffered solutions up to 55 degrees C, and at 70 degrees C was, on average, some 15 to 20 A smaller.
Bovine lens alpha-crystallin in solution can be modeled as a fenestrated spherical shell of diameter 169 A. At physiological temperatures, a weak interaction between alpha- and beta-crystallin occurs, and beta-crystallin is located in the fenestrations. Deuterium substitution indicates that the superaggregation process is controlled by hydrogen bonding. However, the chaperone process and superaggregation appear not to be linked.
Article: The interaction of unfolding α-lactalbumin and malate dehydrogenase with the molecular chaperone αB-crystallin: a light and X-ray scattering investigation.[show abstract] [hide abstract]
ABSTRACT: The molecular chaperone αB-crystallin is found in high concentrations in the lens and is present in all major body tissues. Its structure and the mechanism by which it protects its target protein from aggregating and precipitating are not known. Dynamic light scattering and X-ray solution scattering techniques were used to investigate structural features of the αB-crystallin oligomer when complexed with target proteins under mild stress conditions, i.e., reduction of α-lactalbumin at 37 °C and malate dehydrogenase when heated at 42 °C. In this investigation, the size, shape and particle distribution of the complexes were determined in real-time following the induction of stress. Overall, it is observed that the mass distribution, hydrodynamic radius, and spherical shape of the αB-crystallin oligomer do not alter significantly when it complexes with its target protein. The data are consistent with the target protein being located in the outer protein shell of the αB-crystallin oligomer where it is readily accessible for possible refolding via the action of other molecular chaperones.Molecular vision 01/2010; 16:2446-56. · 2.20 Impact Factor