Multiple molecular architectures of the eye lens chaperone αB-crystallin elucidated by a triple hybrid approach

The molecular chaperone alpha B-crystallin, the major player in maintaining the transparency of the eye lens, prevents stress-damaged and aging lens proteins from aggregation. In nonlenticular cells, it is involved in various neurological diseases, diabetes, and cancer. Given its structural plasticity and dynamics, structure analysis of alpha B-crystallin presented hitherto a formidable challenge. Here we present a pseudoatomic model of a 24-meric alpha B-crystallin assembly obtained by a triple hybrid approach combining data from cryoelectron microscopy, NMR spectroscopy, and structural modeling. The model, confirmed by cross-linking and mass spectrometry, shows that the subunits interact within the oligomer in different, defined conformations. We further present the molecular architectures of additional well-defined alpha B-crystallin assemblies with larger or smaller numbers of subunits, provide the mechanism how "heterogeneity" is achieved by a small set of defined structural variations, and analyze the factors modulating the oligomer equilibrium of alpha B-crystallin and thus its chaperone activity.