Stoichiometry of protein complexes in plant photosynthetic membranes

• Published in: Biochimica et biophysica acta. Bioenergetics 2020-02, Vol.1861 (2), p.148141-148141, Article 148141
• Main Authors: McKenzie, Steven D., Ibrahim, Iskander M., Aryal, Uma K., Puthiyaveetil, Sujith
• Format: Article
• Language: English
• Subjects: Arabidopsis - enzymology; Arabidopsis Proteins - metabolism; Cytochrome b6f; Cytochrome b6f Complex - metabolism; Ferredoxin-quinone reductase; NAD(P)H dehydrogenase; Photosynthesis - physiology; Photosystems; Protein mass spectrometry; Thylakoids; Thylakoids - enzymology
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2019.148141

Hetero-oligomeric membrane protein complexes form the electron transport chain (ETC) of oxygenic photosynthesis. The ETC complexes undertake the light-driven vectorial electron and proton transport reactions, which generate energy-rich ATP and electron-rich NADPH molecules for carbon fixation. The rate of photosynthetic electron transport depends on the availability of photons and the relative abundance of electron transport complexes. The relative abundance of the two photosystems, critical for the quantum efficiency of photosynthesis in changing light quality conditions, has been determined successfully by optical methods. Due to the lack of spectroscopic signatures, however, relatively little is known about the stoichiometry of other non-photosystem complexes in plant photosynthetic membrane. Here we determine the ratios of all major thylakoid-bound ETC complexes in Arabidopsis by a label-free quantitative mass spectrometry technique. The calculated stoichiometries are consistent with known subunit composition of complexes and current estimates of photosystem and cytochrome b6f concentrations. The implications of these stoichiometries for photosynthetic light harvesting and the partitioning of electrons between the linear and cyclic electron transport pathways of photosynthesis are discussed. •A label-free MS approach quantifies the stoichiometries of all plant thylakoid ETC complexes and regulatory proteins•The MS-derived stoichiometries are consistent with values obtained by independent spectroscopic methods•The NDH and FQR ratios have implications for the partitioning of electrons into the linear and cyclic pathways•The relative abundance of regulatory proteins may affect light harvesting, electron transport and protein repair