The Calvin-Benson cycle is the set of chemical reactions that take place in chloroplasts during photosynthesis.  The cycle is light-independent (dark) because it takes place after the energy has been captured from sunlight. It consists of 13 distinct reactions catalysed by 11 enzymes. Among these, the phosphoribulokinase (PRK) had notably still to be characterized at the atomic scale. To accomplish this goal and complete the redox structural proteome of the CB cycle, authors determined the crystal structures of PRK from two model species: the green alga Chlamydomonas reinhardtii (CrPRK) and the land plant Arabidopsis thaliana (AtPRK). Structural comparisons with prokaryotic and evolutionarily older PRKs revealed that both AtPRK and CrPRK have a strongly reduced dimer interface and an increased

number of random coiled regions, suggesting a general loss in structural rigidity during molecular evolution of PRKs in eukaryotes.

Arabidopsis and Chlamydomonas phosphoribulokinase crystal structures complete the redox structural proteome of the Calvin–Bensoncycle;
Gurrieri L., Del Giudice A., Demitri N., Falini G., Viorel Pavel N., Zaffagnini M., Polentarutti M.,  Crozet P., Marchand C. H., Henri J., Trost P., Lemaire S. D., Sparla F., Fermani S.
Proceedings of the National Academy of Sciences Mar 2019, 201820639; DOI: 10.1073/pnas.1820639116