Research on the interaction between cytochrome <italic>b₆f</italic> and ferredoxin-NADP⁺ reductase involved in the cyclic electron transport chain of plant photosynthesis

Aims: In plant photosynthesis, cyclic electron transport (CET) supplies extra ATP to cope with various environmental stresses. However, very little research has been devoted to the CET pathway involving ferredoxin NADP+ reductase (FNR) and cytochrome b6f (Cyt b6f), which maybe a major CET pathway in plants. Methods: In the present study, based on the isolation of the electron transfer proteins including FNR, Cyt b6f and ferredoxin, the CET involving FNR and Cyt b6f was investigated in vitro by spectroscopy, molecular docking and biolayer interferometry. Results: The results of redox different spectra showed that NADPH transferred electrons to Cyt b6f via FNR and ferredoxin, which was dependent on both FNR and ferredoxin. The binding mode of FNR and Cyt b6f was successfully obtained by molecular docking and the optimal Model had a docking score of –244.1 kcal·mol–1 with a high confidence score of 0.867 8. Finally, a dissociation constant (KD) of (43.7±1.32)×10–8 mol·L–1 was detected by biolayer interferometry, showing a moderate-intensity interaction between FNR and Cyt b6f. These results indicated that FNR and Cyt b6f were involved in the plant CET pathway. Conclusion: In conclusion, FNR, as the electron transporter protein at the end of linear electron transport chain, may interact with Cyt b6f and transfer electrons to the latter, forming a CET pathway in plants.