5 years ago

Mechanism of Enzyme Repair by the AAA+ Chaperone Rubisco Activase

Mechanism of Enzyme Repair by the AAA+ Chaperone Rubisco Activase
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.

Graphical abstract



The key photosynthetic enzyme Rubisco undergoes inhibition by substrate and non-substrate sugar phosphates. Inhibited Rubisco requires metabolic repair by the AAA+ chaperone Rubisco activase. Using an integrated approach of biochemical and structural techniques, Bhat et al. show that activase repairs the defective enzyme with remarkable precision, avoiding global structural perturbation.

Publisher URL: www.sciencedirect.com/science

DOI: S1097276517304987

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