Calvin–Benson cycle regulation is getting complex

Two enzymes of the Calvin-Benson cycle, GAPDH and PRK, together with the regulatory protein CP12, can assemble into an inactive multimeric complex.With the recent characterization of the structures of free PRK and GAPDH/CP12/PRK ternary complexes, the hierarchical process of aggregation can be described at molecular definition.• CP12-complexes are conserved in oxygenic phototrophs, but land plants also contain an auto-assembling GAPDH isoform, evolutionary derived from CP12.Both types of complexes form in the dark and dissociate in light, mainly under the control of thioredoxins and pyridine nucleotides.• CP12 is a major light/dark regulator of the Calvin-Benson cycle in cyanobacteria and contributes to the more sophisticated regulation of the cycle in land plants, where dark-complexes may play an additional role in protecting enzymes from proteolysis.