Date: September 8, 16:00〜17:00 (平成28 年9 月8 日（木）)
Venue: Conference room, 1st floor, IMEG (発生医学研究所１階カンファレンス室)
Small heat shock proteins (sHsps) play an important role in proteostasis by preventing the fatalaggregation of denatured proteins. The sHsps are the most ubiquitous molecular chaperones.Structurally, all sHSP share a C-terminal domain, referred to as alpha-crystallin domain, of 80–90 residues consisting of eight beta strands which form an intermolecular beta-sheet interaction site. The sHsps exist as oligomers in unstressed condition. Because the putative interaction sites for denatured proteins, the hydrophobic N-terminal regions locate inside of the oligomeric structures, activation of sHsp is induced by the dissociation of the oligomeric structures. We have been studying the structure and function of sHsps from archaea and eukaryotic cells.
StHsp14.0 of Sulfolobus tokodaii exists as a spherical 24 meric oligomer (1), and the oligomer dissociates to exhibit chaperone function over 80ºC. Small angle X-ray scattering (SAXS) study of StHsp14.0 variants has shown that a partially dissociated oligomer of StHsp14.0 protects a denatured protein (2).
SpHsp16.0 of S. pombe exists as 16mer at the room temperature, and exhibits reversible thermal dissociation of the oligomers to dimers (3). As the nature of unicellular organisms, it is reasonable that SpHap16.0 is directly activated by temperature upshift. We determined the oligomer architecture of SpHsp16.0 with X-ray crystallography and small angle X-ray scattering (4). Both results indicate that eight dimers of SpHsp16.0 form an elongated sphere. The monomers show nonequivalence in the interaction with neighboring monomers and conformations of the N- and C-terminal regions.
There exit various species of sHsps in mammals. Among them, Hsp27, also known as HspB1, is a ubiquitous sHsp. Reflecting the homoiotherm of mammals, it is known that sHsps of mammals are regulated by phosphorylation. To examine the structure and function of Hsp27, we expressed, purified
and characterized Hsp27.0 (CgHsp27) from CHO cell. CgHsp27 forms a monodisperse 16 mer with elongated sphere, which exhibits similar characteristics in temperature dependent conformational change. To examine the effect of phosphorylation, we constructed phosphorylation mimic mutant by
replacing Ser15 to Asp (S15D). The S15D mutant exhibited relatively high temperature sensitivity to express chaperone activity at around the room temperature.
Based on these results, I will discuss a model for the molecular chaperone function of sHsp.
References
1. Hanazono Y et al., J Mol Biol. (2012) 422: 100-108.
2. Abe T et al., J Biochem. (2011) 150: 403-409.
3. Hirose M et al., J Biol Chem. (2005) 280: 32586-32593.
4. Hanazono Y et al., Structure (2013) 21: 220-228.
養王田教授は、今年度「発生医学の研究拠点」事業の共同研究課題に採択されています。
多数のご来聴を歓迎します。
連絡先：分子細胞制御分野 小椋 光（内線6578）
