[WS4] 選抜ワークショップ：微生物の分類・生理・構造・生態/微生物応用

[WS4-4/ODP-034] クライオEMで明らかにしたスピロプラズマ遊泳に関与するらせん状細胞骨格フィブリルの構造

○笹嶋 雄也¹，加藤 貴之²，宮田 知子³，難波 啓一^3,4,5，宮田 真人¹ (¹大阪市大・院理，²阪大・蛋白研，³阪大・院生命機能，⁴理研・BDR & SPring-8，⁵阪大・日本電子YOKOGUSHI協働研)

Spiroplasma are helical-shaped bacteria lacking peptidoglycan, and pathogenic for arthropods and plants. They swim by switching cell helicity between right- and left-handed. We solved the structure of the fibril protein which forms the core part of the swimming machinery by single-particle electron cryomicroscopy last year. This year, we obtained the following new findings. (1) We performed phylogenetic analyses to explore the origin of the fibril acquisition which determined the speciation. The result showed that the fibril protein has evolved from MTA/Adohcy nucleosidase, an enzyme essential for bacterial survival. (2) We revealed another conformation of the fibril filament by single particle analysis to understand the structural changes causing the cell swimming. The fibril protein monomer could be divided into four domains linked by three hinges which can move in three independent angles. The dihedral angles between two domains showed that each of the hinge can give torsions of 2-5 degrees. The integrated torsions can cause changes in the helical pitch and helical diameter as much as two and three folds, respectively, depending on the energy state. Based on these results, we propose a scheme to explain the mechanism of cell swimming as an accumulation of the hinge movements.