The small heat-shock protein (sHsp) chaperones play important roles in the cell by preventing aggregation of destabilized proteins. In plants, the sHsps confer an especially pronounced and important part of the stress response, with several sHsp paralogues being present in different cell compartments, heat-induced or developmentally regulated. Hsp21 is a chloroplast located small heat shock protein. A structure model of Hsp21, obtained by homology modeling, single-particle electron microscopy, and lysine-specific chemical crosslinking, shows that the Hsp21 subunits are arranged in two hexameric discs, rotated by 25 degree in relation to each other.
