Overexpression of the RieskeFeS protein increases electron transport rates and biomass yield. Improving photosynthetic efficiency for greater yield. Ferredoxin:NADP + oxidoreductase is a subunit of the chloroplast cytochrome b 6 f complex. Dynamic thylakoid stacking regulates the balance between linear and cyclic photosynthetic electron transfer. Chloroplast protein phosphorylation couples plastoquinone redox state to distribution of excitation energy between photosystems. Interaction between light harvesting chlorophyll- a/ b protein (LHCII) kinase and cytochrome b 6/ f complex. Plastoquinol at the quinol oxidation site of reduced cytochrome bf mediates signal transduction between light and protein phosphorylation: thylakoid protein kinase deactivation by a single-turnover flash. The basis of state I–state II transitions in chloroplasts. Activation of adenosine 5′-triphosphate induced quenching of chlorophyll fluorescence by reduced plastoquinone.
Physiological functions of cyclic electron transport around photosystem I in sustaining photosynthesis and plant growth. State transitions and light adaptation require chloroplast thylakoid protein kinase STN7. Structure–function, stability, and chemical modification of the cyanobacterial cytochrome b 6 f complex from Nostoc sp. Structure of the cytochrome b 6 f complex of oxygenic photosynthesis: tuning the cavity. An atypical haem in the cytochrome b 6 f complex. Understanding the cytochrome bc complexes by what they don’t do. Inhibitor-complexed structures of the cytochrome bc 1 from the photosynthetic bacterium Rhodobacter sphaeroides. Crystal structure of the cytochrome bc 1 complex from bovine heart mitochondria. The cytochrome b 6 f complex at the crossroad of photosynthetic electron transport pathways. The Q cycle of cytochrome bc complexes: a structure perspective. Function of the two cytochrome components in chloroplasts: a working hypothesis. The spinach cyt b 6 f structure therefore provides new insights into how the complex fulfils its catalytic and regulatory roles in photosynthesis. The location of a tentatively assigned third PQ molecule is consistent with a transition between the Q p and Q n sites in opposite monomers during the Q cycle. A conformational switch involving the haem c n propionate promotes two-electron, two-proton reduction at the Q n site and avoids formation of the reactive intermediate semiquinone.
PQ2 straddles the intermonomer cavity, partially obstructing the PQ reduction site (Q n) on the PQ1 side and committing the electron transfer network to turnover at the occupied Q n site in the neighbouring monomer. Two conformations of the chlorophyll a phytyl tail were resolved, one that prevents access to the Q p site and another that permits it, supporting a gating function for the chlorophyll a involved in redox sensing. The first, PQ1, is located in one cyt b 6 f monomer near the PQ oxidation site (Q p) adjacent to haem b p and chlorophyll a. The complex contains up to three natively bound PQ molecules. Here we present a 3.6 Å resolution cryo-electron microscopy (cryo-EM) structure of the dimeric cyt b 6 f complex from spinach, which reveals the structural basis for operation of the Q cycle and its redox-sensing function. In higher plants, cyt b 6 f also acts as a redox-sensing hub, pivotal to the regulation of light harvesting and cyclic electron transfer that protect against metabolic and environmental stresses 3.
Electron transfer within cyt b 6 f occurs via the quinol (Q) cycle, which catalyses the oxidation of plastoquinol (PQH 2) and the reduction of both plastocyanin (PC) and plastoquinone (PQ) at two separate sites via electron bifurcation 2. The cytochrome b 6 f (cyt b 6 f ) complex has a central role in oxygenic photosynthesis, linking electron transfer between photosystems I and II and converting solar energy into a transmembrane proton gradient for ATP synthesis 1, 2, 3.