Physicochemical characterization of gamma-crystallins from bovine lens--hydrodynamic and biochemical properties

A detailed hydrodynamic study has been made on the gamma-crystallin of the bovine lens. Sedimentation study indicates that gamma-crystallin shows a nearly gaussian peak throughout the course of sedimentation at high speed, using a synthetic boundary cell. The diffusion and sedimentation coefficients are 10.3 x 10(-7) cm2/sec and 2.51 S, respectively. The weight-average molecular weight of the unfractionated gamma-crystallin calculated from sedimentation equilibrium is 21,800. The four major subfractions of gamma-crystallin show similar hydrodynamic properties with an intrinsic viscosity of 2.50 ml/g and a Stokes radius of 21 A. The distinct electrophoretic mobilities exhibited by the four subfractions show gel-concentration dependence and similar slopes in the Ferguson plot, indicative of being charge isomers of the same molecular species. Amino acid analysis of these four subfractions corroborated the conclusions that these gamma-crystallin polypeptides are closely related and comprise a multigene family of crystallins. Based on the sedimentation and intrinsic viscosity data, gamma-crystallin can be modeled as a prolate ellipsoid with an axial ratio of approximately 3.0 and a hydration factor of 0.27 g water per gram protein. The circular dichroism data for gamma-crystallins showed a minimum at about 217 nm, characteristic of a beta-sheet conformation. These structural characteristics are in good accord with those derived from X-ray diffraction data for gamma-crystallin II.