ジャーナル: Mol Cell / 年: 2017 タイトル: Mechanism of Enzyme Repair by the AAA Chaperone Rubisco Activase. 著者: Javaid Y Bhat / Goran Miličić / Gabriel Thieulin-Pardo / Andreas Bracher / Andrew Maxwell / Susanne Ciniawsky / Oliver Mueller-Cajar / John R Engen / F Ulrich Hartl / Petra Wendler / Manajit Hayer-Hartl / 要旨: How AAA+ chaperones conformationally remodel specific target proteins in an ATP-dependent manner is not well understood. Here, we investigated the mechanism of the AAA+ protein Rubisco activase (Rca) ...How AAA+ chaperones conformationally remodel specific target proteins in an ATP-dependent manner is not well understood. Here, we investigated the mechanism of the AAA+ protein Rubisco activase (Rca) in metabolic repair of the photosynthetic enzyme Rubisco, a complex of eight large (RbcL) and eight small (RbcS) subunits containing eight catalytic sites. Rubisco is prone to inhibition by tight-binding sugar phosphates, whose removal is catalyzed by Rca. We engineered a stable Rca hexamer ring and analyzed its functional interaction with Rubisco. Hydrogen/deuterium exchange and chemical crosslinking showed that Rca structurally destabilizes elements of the Rubisco active site with remarkable selectivity. Cryo-electron microscopy revealed that Rca docks onto Rubisco over one active site at a time, positioning the C-terminal strand of RbcL, which stabilizes the catalytic center, for access to the Rca hexamer pore. The pulling force of Rca is fine-tuned to avoid global destabilization and allow for precise enzyme repair.
RcaCC hexamers (20 micromolar monomer) were mixed with E.C.M-CABP octamers (10 micromolar monomer) in a reaction containing 20 mM HEPES pH 7.5, 50 mM NaCl, 10 mM MgCl2, 10 mM ATP and 1mM RuBP, for 1 min at 25oC prior to addition of 0.125 % of glutaraldehyde (GA). After 10 min the reaction was quenched by addition of 0.1M Tris HCl pH 8 followed by gel filtration on a Superdex 200 PC 3.2/30 column (GE Healthcare).The fractions were eluted in buffer A and analyzed on a 6 % native gel. Fraction 13 containing HMW complexes with the least amount of free Rubisco were chosen for cryo-EM. The crosslinked E.C.M.-CABP-RcaCC complexes were diluted to 0.0030-0.0035 g ml-1 in 20 mM Tris-HCl pH 8.0, 50 mM NaCl, 1 mM ATP, 1 mM ATP-gammaS and 1 mM RuBP
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電子顕微鏡法
顕微鏡
FEI TITAN KRIOS
詳細
Cs corrected Krios 1 at NeCEN (June 2016)
撮影
フィルム・検出器のモデル: FEI FALCON II (4k x 4k) 平均露光時間: 1.25 sec. / 平均電子線量: 50.0 e/Å2