Alpha crystallin domain (ACD) found in Saccharomyces cerevisiae (Sc) small heat shock protein (Hsp)26 and similar proteins. sHsps are molecular chaperones that suppress protein aggregation and protect against cell stress, and are generally active as large oligomers consisting of multiple subunits. ScHsp26 is temperature-regulated, it switches from an inactive to a chaperone-active form upon elevation in temperature. It associates into large 24-mers storage forms which upon heat shock disassociate into dimers. These dimers initiate the interaction with non-native substrate proteins and re-assemble into large globular assemblies having one monomer of substrate bound per dimer. This group also contains Arabidopsis thaliana (Ath) Hsp15.7, a peroxisomal matrix protein which can complement the morphological phenotype of S. cerevisiae mutants deficient in Hsps26. AthHsp15.7 is minimally expressed under normal conditions and is strongly induced by heat and oxidative stress. Also belonging to this group is wheat HSP16.9 which differs in quaternary structure from the shell-type particles of ScHsp26, it assembles as a dodecameric double disc, with each disc organized as a trimer of dimers.
Structure:2H50, Saccharomyces cerevisiae Hsp26 dimer interface, contacts at 3.5 A - View structure with Cn3D
Comment:ScHsp26 assembles in shell-like particles composed of 24 subunits. These particles are storage forms which upon heat shock disassociate into dimers. Non-native substrate proteins bind the disassociated ScHsp26 and assemble into large globular assemblies having one monomer of substrate bound per dimer.