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Structural basis of light-induced redox regulation in the Calvin–Benson cycle in cyanobacteria

DOI: 10.1073/pnas.1906722116 DOI Help

Authors: Ciaran R. Mcfarlane (Imperial College London) , Nita R. Shah (Imperial College London) , Burak V. Kabasakal (Imperial College London) , Blanca Echeverria (Imperial College London) , Charles Cotton (Imperial College London) , Doryen Bubeck (University of Oxford) , James W. Murray (Imperial College London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Proceedings Of The National Academy Of Sciences , VOL 75

State: Published (Approved)
Published: September 2019
Diamond Proposal Number(s): 19432 , 18659 , 12579

Open Access Open Access

Abstract: Plants, algae, and cyanobacteria fix carbon dioxide to organic carbon with the Calvin–Benson (CB) cycle. Phosphoribulokinase (PRK) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) are essential CB-cycle enzymes that control substrate availability for the carboxylation enzyme Rubisco. PRK consumes ATP to produce the Rubisco substrate ribulose bisphosphate (RuBP). GAPDH catalyzes the reduction step of the CB cycle with NADPH to produce the sugar glyceraldehyde 3-phosphate (GAP), which is used for regeneration of RuBP and is the main exit point of the cycle. GAPDH and PRK are coregulated by the redox state of a conditionally disordered protein CP12, which forms a ternary complex with both enzymes. However, the structural basis of CB-cycle regulation by CP12 is unknown. Here, we show how CP12 modulates the activity of both GAPDH and PRK. Using thermophilic cyanobacterial homologs, we solve crystal structures of GAPDH with different cofactors and CP12 bound, and the ternary GAPDH-CP12-PRK complex by electron cryo-microscopy, we reveal that formation of the N-terminal disulfide preorders CP12 prior to binding the PRK active site, which is resolved in complex with CP12. We find that CP12 binding to GAPDH influences substrate accessibility of all GAPDH active sites in the binary and ternary inhibited complexes. Our structural and biochemical data explain how CP12 integrates responses from both redox state and nicotinamide dinucleotide availability to regulate carbon fixation.

Journal Keywords: redox regulation; carbon fixation; photosynthesis; Calvin–Benson cycle

Subject Areas: Biology and Bio-materials, Chemistry

Diamond Offline Facilities: Electron Bio-Imaging Centre (eBIC)
Instruments: I02-Macromolecular Crystallography , I03-Macromolecular Crystallography , I04-Macromolecular Crystallography , I24-Microfocus Macromolecular Crystallography , Krios I-Titan Krios I at Diamond

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