Hsp33 is a molecular chaperone, distinguished from all other known chaperones by its mode of functional regulation. Its activity is redox regulated. Hsp33 is a cytoplasmically localised protein with highly reactive cysteines that respond quickly to changes in the redox environment. Oxidising conditions like H2O2 cause disulfide bonds to form in Hsp33, a process that leads to the activation of its chaperone function [1].

1: Chaperone activity with a redox switch. Jakob U, Muse W, Eser M, Bardwell JC; Cell 1999;96:341-352. PMID:10025400

2: The 2.2 A crystal structure of Hsp33: a heat shock protein with redox-regulated chaperone activity. Vijayalakshmi J, Mukhergee MK, Graumann J, Jakob U, Saper MA; Structure (Camb) 2001;9:367-375. PMID:11377197