ジャーナル: Nature / 年: 2024 タイトル: Visualizing chaperonin function in situ by cryo-electron tomography. 著者: Jonathan Wagner / Alonso I Carvajal / Andreas Bracher / Florian Beck / William Wan / Stefan Bohn / Roman Körner / Wolfgang Baumeister / Ruben Fernandez-Busnadiego / F Ulrich Hartl / 要旨: Chaperonins are large barrel-shaped complexes that mediate ATP-dependent protein folding. The bacterial chaperonin GroEL forms juxtaposed rings that bind unfolded protein and the lid-shaped cofactor ...Chaperonins are large barrel-shaped complexes that mediate ATP-dependent protein folding. The bacterial chaperonin GroEL forms juxtaposed rings that bind unfolded protein and the lid-shaped cofactor GroES at their apertures. In vitro analyses of the chaperonin reaction have shown that substrate protein folds, unimpaired by aggregation, while transiently encapsulated in the GroEL central cavity by GroES. To determine the functional stoichiometry of GroEL, GroES and client protein in situ, here we visualized chaperonin complexes in their natural cellular environment using cryo-electron tomography. We find that, under various growth conditions, around 55-70% of GroEL binds GroES asymmetrically on one ring, with the remainder populating symmetrical complexes. Bound substrate protein is detected on the free ring of the asymmetrical complex, defining the substrate acceptor state. In situ analysis of GroEL-GroES chambers, validated by high-resolution structures obtained in vitro, showed the presence of encapsulated substrate protein in a folded state before release into the cytosol. Based on a comprehensive quantification and conformational analysis of chaperonin complexes, we propose a GroEL-GroES reaction cycle that consists of linked asymmetrical and symmetrical subreactions mediating protein folding. Our findings illuminate the native conformational and functional chaperonin cycle directly within cells.
凍結剤: ETHANE-PROPANE / チャンバー内湿度: 100 % / チャンバー内温度: 277 K / 装置: FEI VITROBOT MARK IV 詳細: 5.9 mM n-octyl-beta-D-glucopyranoside were added before vitrification.
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電子顕微鏡法
顕微鏡
FEI TITAN KRIOS
撮影
フィルム・検出器のモデル: GATAN K3 (6k x 4k) / 平均電子線量: 55.0 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 / 最大 デフォーカス(公称値): 3.0 µm / 最小 デフォーカス(公称値): 0.5 µm / 倍率(公称値): 22500
実験機器
モデル: Titan Krios / 画像提供: FEI Company
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画像解析
初期モデル
モデルのタイプ: INSILICO MODEL / In silico モデル: CryoSparc ab initio