Physicochemical characterization of gamma-crystallins from bovine lens--hydrodynamic and biochemical properties |
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Authors: | Shyh-Horng Chiou Parviz Azari and Michael E Himmel |
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Institution: | (1) Institute of Biological Chemistry, Academia Sinica, P.O. Box 23-106, Taipei, Taiwan, R.O.C.;(2) Department of Biochemistry, Colorado State University, 80523 Fort Collins, Colorado;(3) Biotechnology Branch, Solar Energy Research Institute (SERI), Golden, Colorado |
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Abstract: | A detailed hydrodynamic study has been made on the -crystallin of the bovine lens. Sedimentation study indicates that -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 10.3×10–7 cm2/sec and 2.51 S, respectively. The weight-average molecular weight of the unfractionated -crystallin calculated from sedimentation equilibrium is 21,800. The four major subfractions of -crystallin show similar hydrodynamic properties with an intrinsic viscosity of 2.50 ml/g and a Stokes radius of 21 Å. 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 -crystallin polypeptides are closely related and comprise a multigene family of crystallins. Based on the sedimentation and intrinsic viscosity data, -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 -crystallins showed a minimum at about 217 nm, characteristic of a -sheet conformation. These structural characteristics are in good accord with those derived from X-ray diffraction data for -crystallin II. |
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Keywords: | lens crystallins sedimentation equilibrium intrinsic viscosity protein sequences microheterogeneity circular dichroism |
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