Physicochemical characterization of alpha-crystallins from bovine lenses: hydrodynamic and conformational properties.
A detailed investigation of hydrodynamic and conformational behavior has been made of the HM alpha-crystallin and alpha-crystallins of bovine lens. Results from this study indicated that HM alpha (high-molecular-weight alpha-crystallin) and alpha (low-molecular-weight alpha-crystallin) possess considerable size and charge heterogeneities in their native structures and subunit polypeptides, respectively. Sedimentation velocity showed a heterogeneous polydisperse system of HM alpha with an average sedimentation coefficient of about 50S and a more homogeneous system of alpha-crystallin of 20 S. Viscosity and circular dichroism studies pointed to a compact and globular shape of dominant beta-sheet conformation for alpha-crystallin, yet a highly asymmetrical and aggregated form for HM alpha. The conformational stability of alpha-crystallin was investigated in the presence of various denaturants. The evidence presented shows that hydrogen bonding is the main force in maintaining the quaternary structure of compact native alpha-crystallin. Conformational flexibility of alpha-crystallin demonstrated in the equilibrium unfolding study indicated a multistep transition that made the extraction of thermodynamic data from the heat denaturation study difficult. Temperature perturbation on alpha-crystallin suggested the possible involvement of hydrophobic interaction in the aggregation process, leading to the formation of HM alpha from alpha-crystallin. The comparison of conformational properties between HM alpha and alpha-crystallin strongly indicated that HM alpha is a denatured form of alpha-crystallin.
Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan, ROC.
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D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D002845:Chromatography / Q000379:methods; D002942:Circular Dichroism; D003459:Crystallins / Q000302:isolation & purification*; D006860:Hydrogen Bonding; D007908:Lens, Crystalline / Q000032:analysis*; D008970:Molecular Weight; D011487:Protein Conformation; D011489:Protein Denaturation; D013696:Temperature; D014461:Ultracentrifugation; D014783:Viscosity
D000596:Amino Acids; D003459:Crystallins