ジャーナル: Proc Natl Acad Sci U S A / 年: 2016 タイトル: A ring-shaped conduit connects the mother cell and forespore during sporulation in Bacillus subtilis. 著者: Christopher D A Rodrigues / Xavier Henry / Emmanuelle Neumann / Vilius Kurauskas / Laure Bellard / Yann Fichou / Paul Schanda / Guy Schoehn / David Z Rudner / Cecile Morlot / 要旨: During spore formation in Bacillus subtilis a transenvelope complex is assembled across the double membrane that separates the mother cell and forespore. This complex (called the "A-Q complex") is ...During spore formation in Bacillus subtilis a transenvelope complex is assembled across the double membrane that separates the mother cell and forespore. This complex (called the "A-Q complex") is required to maintain forespore development and is composed of proteins with remote homology to components of type II, III, and IV secretion systems found in Gram-negative bacteria. Here, we show that one of these proteins, SpoIIIAG, which has remote homology to ring-forming proteins found in type III secretion systems, assembles into an oligomeric ring in the periplasmic-like space between the two membranes. Three-dimensional reconstruction of images generated by cryo-electron microscopy indicates that the SpoIIIAG ring has a cup-and-saucer architecture with a 6-nm central pore. Structural modeling of SpoIIIAG generated a 24-member ring with dimensions similar to those of the EM-derived saucer. Point mutations in the predicted oligomeric interface disrupted ring formation in vitro and impaired forespore gene expression and efficient spore formation in vivo. Taken together, our data provide strong support for the model in which the A-Q transenvelope complex contains a conduit that connects the mother cell and forespore. We propose that a set of stacked rings spans the intermembrane space, as has been found for type III secretion systems.
凍結剤: ETHANE / チャンバー内湿度: 100 % / 装置: FEI VITROBOT MARK IV
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電子顕微鏡法
顕微鏡
FEI POLARA 300
撮影
フィルム・検出器のモデル: KODAK SO-163 FILM / 平均電子線量: 15.0 e/Å2
電子線
加速電圧: 300 kV / 電子線源: FIELD EMISSION GUN
電子光学系
照射モード: OTHER / 撮影モード: BRIGHT FIELD / Cs: 2.0 mm
試料ステージ
ホルダー冷却材: NITROGEN
実験機器
モデル: Tecnai Polara / 画像提供: FEI Company
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画像解析
CTF補正
ソフトウェア - 名称: CTFFIND
初期モデル
モデルのタイプ: OTHER 詳細: The initial model was generated by back-projecting a side view and imposing C24 symmetry (as determined by ultracentrifugation experiments)
最終 再構成
想定した対称性 - 点群: C24 (24回回転対称) / アルゴリズム: BACK PROJECTION / 解像度のタイプ: BY AUTHOR / 解像度: 35.0 Å / 解像度の算出法: FSC 0.5 CUT-OFF / 使用した粒子像数: 6125