Catchers of folding gone awry: a tale of small heat shock proteins

Small heat shock proteins (sHsps) are an important part of the cellular system maintaining protein homeostasis under physiological and stress conditions. As molecular chaperones, they form complexes with different non-native proteins in an ATP-independent manner. Many sHsps populate ensembles of energetically similar but different-sized oligomers. Regulation of chaperone activity occurs by changing the equilibrium of these ensembles. This makes sHsps a versatile and adaptive system for trapping non-native proteins in complexes, allowing recycling with the help of ATP-dependent chaperones. In this review, we discuss progress in our understanding of the structural principles of sHsp oligomers and their functional principles, as well as their roles in aging and eye lens transparency.