Temperature dependence of chaperone-like activity and oligomeric state of αB-crystallin

The chaperone-like activity and the oligomeric state of αB-crystallin were studied at different temperatures and in the presence of urea and thiocyanate. The activity, assessed measuring the ability of αB-crystallin to prevent the aggregation of denatured insulin, strongly depends on temperature. While a significant activity increase was detected at 42 °C, the presence of urea and thiocyanate does not affect the protein activity in an irreversible way. In-solution SAXS measurements performed in the same experimental conditions showed that αB-crystallin forms near-spherical, hollowed, polydisperse oligomers, whose dimensions change above 42 °C. Moreover, in the presence of urea and thiocyanate, a global fit analysis confirms the high stability of αB-crystallin assemblies in relationship with their variable quaternary structure. In particular, the changes in the inner radius as well as the thickness and dispersion of the protein shell, account for the preservation of the chaperone-like activity.