Related Experiment Video
Updated: Jul 10, 2026
13:52
Studying the Supramolecular Organization of Photosynthetic Membranes within Freeze-fractured Leaf Tissues by Cryo-scanning Electron Microscopy
Published on: June 23, 2016
Cryo-EM structures of naturally occurring dimeric photosystem II complexes lacking the Mn4CaO5 cluster
Ziyu Zhao1,2, Irene Vercellino1,3, Julian P Whitelegge4
1Institute of Science and Technology Austria, Klosterneuburg, Austria.
Nature Communications
|July 8, 2026
Summary
Researchers reveal structures of photosystem II (PSII) intermediates, uncovering how the oxygen-evolving complex assembles and disassembles. This provides insights into photosynthesis regulation and repair mechanisms in cyanobacteria.
Area of Science:
- Biochemistry
- Structural Biology
- Photosynthesis Research
Background:
- Oxygenic photosynthesis relies on the precise assembly and repair of photosystem II (PSII).
- Previous structural studies of PSII intermediates often used deletion mutants or in vitro subunit removal.
- Understanding PSII assembly is crucial for efficient energy conversion and cellular repair.
Purpose of the Study:
- To determine the high-resolution structures of naturally occurring dimeric PSII assembly/disassembly intermediates.
- To elucidate the mechanism of oxygen-evolving complex (OEC) assembly and disassembly.
- To investigate the role of extrinsic proteins and D1 subunit restructuring in PSII regulation.
Main Methods:
- Cryo-electron microscopy (cryo-EM) at approximately 2.2 Å resolution.
- Analysis of naturally occurring dimeric PSII intermediates from Thermosynechococcus vestitus.
- Integration of mass spectrometry data.
Main Results:
- Reported cryo-EM structures of inactive and semi-active dimeric PSII intermediates.
- Revealed a mechanism coordinating Mn4CaO5 cluster assembly/disassembly with extrinsic protein binding/release.
- Identified potential damage in inactive PSII complexes involving oxidized D1-His332.
Conclusions:
- The C-terminal tail of the D1 subunit plays a key role in regulating PSII assembly and disassembly.
- Conformational changes in D2, CP47, and CP43 are triggered by D1 restructuring.
- Structural insights into PSII repair mechanisms and potential damage pathways.
Related Concept Videos
01:32Photosystems
Photosystems are multiprotein complexes that form the functional units of photosynthesis in plants, algae, and cyanobacteria. They are found embedded in the membrane of tiny sac-like structures called thylakoids placed inside the chloroplast.
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
01:22Photosystem II
The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
01:27Photosystem I
Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
01:28Cryo-electron Microscopy
Conventional electron microscopy (EM) involves dehydration, fixation, and staining of biological samples, which distorts the native state of biological molecules and results in several artifacts. Also, the high-energy electron beam damages the sample and makes it difficult to obtain high-resolution images. These issues can be addressed using cryo-EM, which uses frozen samples and gentler electron beams. The technique was developed by Jacques Dubochet, Joachim Frank, and Richard Henderson, for...
01:29The Photochemical Reaction Center
Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...
01:43Electron Transport Chain: Complex III and IV
During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...