Structure of an enzyme that controls photosynthetic carbon fixation in response to light
What is it about?
In photosynthetic organisms, carbon fixation must be coordinated with the light reaction to prevent unnecessary energy expenditure in absence of light. The enzyme phosphoribulokinase produces the substrate for the carbon fixation step and switches off reversibly by disulfide bond formation. How this works in cyanobacteria is reported in the paper.
Why is it important?
Photosynthesis researchers realized early on that the activity of phosphoribulokinase (PRK, E.C. 2.7.1.19) from plants, algae and cyanobacteria is regulated by reversible disulfide bond formation, but structural data for this important Calvin cycle enzyme were missing. Our data show that the fold of the photosynthetic enzymes differs considerably from the PRK enzymes from non-photosynthetic bacteria and archaea. These results were independently confirmed by a parallel study on the structures of PRK from plants and green algae by Gurrieri and coworkers. In addition, our structure of the PRK orthologue from the cyanobacterium Synechococcus sp. strain PCC 6301 revealed the long-sought structure of the redox-blocked state.