Redefining the chaperone mechanism of sHsps: not just holdase chaperones
The small heat-shock proteins (sHsps) are molecular chaperones that play a fundamental role in maintaining cellular protein homeostasis (proteostasis) by preventing the aggregation of destabilised proteins. They are generally described as 'holdase' type chaperones since they have the ability to bind partially folded intermediate states of target proteins, in an ATP-independent manner, and, in doing so, they can form high molecular weight complexes with some of them. However, recent work has shown that the ability of sHsps to interact with target proteins is multi-faceted. This review highlights the mechanisms by which sHsps can interact with aggregation-prone target proteins and proposes that they should be considered as protein 'stabilisers' rather than 'holdase' chaperones.