A smallâangle Xâray solution scattering study of bovine αâcrystallin
2000
Vanhoudt, Jos | Abgar, Saı¨d | Aerts, Tony | Clauwaert, Julius
The native high molecular mass form of αâcrystallin, the most important soluble protein in the eye lens, and its low molecular mass form obtained at 37â°C in dilute solutions were investigated by synchrotron radiation smallâangle Xâray scattering. The αâcrystallin solutions are polydisperse and good fits to the experimental data can be obtained using distributions of spheres with radii varying between about 5 and 10ânm. In spite of the polydispersity, two different ab initio methods were used to retrieve low resolution shapes from the scattering data. These shapes correspond to the zâaverage structure of the oligomers. In the absence of any symmetry constraints, the scattering curves of the two forms of αâcrystallin yield beanâlike shapes. The shape corresponding to the low molecular mass form has about 20% less mass at the periphery. Imposing tetrahedral symmetry on the average structures worsens the fit to the experimental data. We emphasized the apparent contradiction between hydrodynamic and molecular properties of αâcrystallin. An explanation was put forward based on the presence of solventâexposed flexible Câterminal extensions. We present two bead models (‘hollow globule with tentacles’ and ‘bean with tentacles’) based on NMR and cryoâelectron microscopy studies and discuss how well they correspond with our data from Xâray scattering, light scattering and analytical ultracentrifugation.
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