Mainly structural but also some functional insights into the unique CBS–CP12 fusion protein family in cyanobacteria

by Dr Johanna Hakanpää (DESY)

109 (25b)



Cyanobacteria are important photosynthetic organisms inhabiting a range of dynamic environments. This phylum is distinctive among photosynthetic organisms in containing genes encoding uncharacterized cystathionine β-synthase (CBS)–chloroplast protein (CP12) fusion proteins. These consist of two domains, each recognized as stand-alone photosynthetic regulators with different functions described in cyanobacteria (CP12) and plants (CP12 and CBSX). In our study focusing on a CBS–CP12 from Microcystis aeruginosa, we reveal that the domain fusion led to the formation of a hexameric protein. We show that the CP12 domain contains an ordered, previously structurally uncharacterized N-terminal region. We provide evidence that CBS–CP12, while combining properties of both regulatory domains, behaves different from CP12 and plant CBSX. It does not form a ternary complex with phosphoribulokinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase. Instead, CBS–CP12 decreases the activity of PRK in an AMP-dependent manner. We propose that the novel domain architecture and oligomeric state of CBS–CP12 expand its regulatory function beyond those of CP12 in cyanobacteria. 1) Hackenberg C., Hakanpää J., Cai F., Antonyuk S., Eigner C., Meissner S., Laitaoja M., Jänis J., Kerfeld C.A., Dittmann E., Lamzin V.S. (2018) Proc Natl Acad Sci 115 7141-7146.