3D structure of the native α-crystallin from bovine eye lens

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α-Crystallin is the major eye lens protein that has been shown to support lens transparency by preventing the aggregation of lens proteins. The 3D structure of α-crystallin is largely unknown.Electron microscopy, single-particle 3D reconstruction, size exclusion chromatography, dynamic light scattering, and analytical ultracentrifugation were used to study the structure of the native α-crystallin. Native α-crystallin has a wide distribution in size. The shape of mass distribution is temperature-dependent, but the oligomers with a sedimentation coefficient of ~22 S (750–830 kDa) strongly prevailed at all temperatures used. A 3D model of native α-crystallin with resolution of ~2 nm was created. The model is asymmetrical, has an elongated bean-like shape 13 × 19 nm with a dense core and filamentous “kernel”. It does not contain a central cavity. The majority of α-crystallin particles regardless of experimental conditions are 13 × 19 nm, which corresponds to 22S sedimentation coefficient, hydrodynamic diameter 20 nm and mass of 750–830 kD. These particles are in dynamic equilibrium with particles of smaller and larger sizes.