The Quaternary Structure of Bovine alpha-Crystallin. Size and Shape Studies by Sedimentation, Small-angle X-Ray Scattering and Quasi-elastic Light Scattering

Physicochemical properties of native and reassociated α-crystallin populations from calf lens cortex have been determined at pH = 7.3 and ionic strength 0.1 M. Sedimentation analysis of native and reassociated α-crystallin gives molecular weights of 854000 and 430000, sedimentation coefficients of 19.2 S and 13.4 S, frictional ratios of 1.54 and 1.39, and Stokes radii of 9.7 nm and 7.0 nm respectively. Small-angle X-ray scattering of native and reassociated α-crystallin gives radii of gyration of 6.2 and 5.1 nm, molecular weights of 837000 and 420000, hydrated volumes of 1552 nm3 and 805 nm3, and hydration values of 0.38 and 0.41 g H2O/g protein respectively. The scattering curves indicate near-spherical symmetry. Distance distribution functions and radial electron densities have been calculated. Very distinct maxima in the circularly integrated diffraction patterns of pellets indicate a semi-crystalline orientation of the molecules, with a periodicity of 15.4 nm and 12.8 nm for native and reassociated α-crystallin respectively. Quasi-elastic light scattering gives diffusion coefficients of 2.55 × 10−7 and 2.94 × 10−7 cm2/s, Stokes radii of 8.3 nm and 7.2 nm, and frictional ratios of 1.31 and 1.43 for native and reassociated α-crystallin. All the hydrodynamic data are in agreement with a quasi-spherical shap of both native and reassociated α-crystallin, and diameters of 16.1 × 0.7 nm and 13.3 × 0.9 nm. This agrees with our previous electron microscopic observations, albeit the diameters are 10–20% smaller in the electron microscope, possible due to dehydration.