Studies of α- and β_L-Crystallin Complex Formation in Solution at 60°C

Abstract

Studies of molecular mechanisms of chaperone-like activity of α-crystallin became an active field of research over last years. However, fine interactions between α-crystallin and the damaged protein and their complex organization remain largely uncovered. Complexation between α- and β_L-crystallins was studied during thermal denaturation of β_L-crystallin at 60°C using small-angle X-ray scattering (SAXS), light scattering, gel-permeation chromatography, and electrophoresis. A mixed solution of α- and β_L-crystallins at concentrations about 10 mg/ml incubated at 60°C was found to contain their soluble complexes with a mean radius of gyration ∼14 nm, mean molecular mass ∼4 MDa and maximal size over 40 nm. In pure β_L-crystallin solution, no complexes were observed at 60°C. In SAXS studies, transitions in the α-crystallin quaternary structure at 60°C were shown to occur and result in doubling of the molecular weight. This suggests that during the temperature-induced denaturation of β_L-crystallin it binds with modified α-crystallin or, alternatively, β_L-crystallin complexation and α-crystallin modifications are concurrent. Estimates of the α-β_L-crystallin complex size and relative contents of α- and α-β_L-crystallins in the complex suggest that several α-crystallin molecules are involved in complex formation.