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Bhat, Javaid Y.; Milicic, Goran; Thieulin-Pardo, Gabriel; Bracher, Andreas; Maxwell, Andrew; Ciniawsky, Susanne; Müller-Cajar, Oliver; Engen, John R.; Hartl, F. Ulrich; Wendler, Petra; Hayer-Hartl, Manajit (2017): Mechanism of Enzyme Repair by the AAA(+) Chaperone Rubisco Activase. In: Molecular Cell, Vol. 67, No. 5: pp. 744-756
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Abstract

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.