11:28 AM - 11:42 AM
[WS4-08] Study on the temperature-dependent oligomer dissociation mechanism of the small heat shock proteins using those from Methanogenic archaea
Small heat shock protein (sHsp) is a ubiquitous molecular chaperone that endows the cell with stress tolerance. The common feature of sHsps is the α-crystallin domain, named after the α-crystallin in vertebrate lenses. The N-terminal region is highly variable, and the C-terminal extension is partially conserved with the consensus IXI motif. Most sHsps take large oligomeric structures composed of 12 - 36 subunits and dissociate when exposed to stress, such as high temperature, to expose a hydrophobic region and capture the denatured protein to prevent aggregation. However, the mechanism for temperature-dependent oligomer dissociation has not been elucidated. Methanogenic archaea grow in various environments. The optimal growth temperature of Methanocaldococcus jannaschii is 85°C, and that of Methanococcus maripaludis is 38°C. Their sHsps (MJsHsp and MMsHsp) share significantly high amino acid sequence homology except for the N-terminus but differ significantly in temperature dependence. To verify whether the N-terminal domain determines temperature sensitivity, we created chimera mutants in which the N-terminal domain is exchanged and analyzed their temperature-dependent dissociation. Contrary to our expectation, the N-terminal domain is not related to the temperature sensitivity. Then, we compared amino acid sequences among various methanogenic sHsps and found several amino acid residues that are different between mesophilic and hyperthermophilic ones. We will report the effect of mutations of these residues on the temperature dependency and the chaperone activity.