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Review
. 2022 Apr 19;10(5):836.
doi: 10.3390/microorganisms10050836.

Advances in the Understanding of the Lifecycle of Photosystem II

Virginia M Johnson  1 , Himadri B Pakrasi  1
Affiliations
Review

Advances in the Understanding of the Lifecycle of Photosystem II

Virginia M Johnson et al. Microorganisms. .

Abstract

Photosystem II is a light-driven water-plastoquinone oxidoreductase present in cyanobacteria, algae and plants. It produces molecular oxygen and protons to drive ATP synthesis, fueling life on Earth. As a multi-subunit membrane-protein-pigment complex, Photosystem II undergoes a dynamic cycle of synthesis, damage, and repair known as the Photosystem II lifecycle, to maintain a high level of photosynthetic activity at the cellular level. Cyanobacteria, oxygenic photosynthetic bacteria, are frequently used as model organisms to study oxygenic photosynthetic processes due to their ease of growth and genetic manipulation. The cyanobacterial PSII structure and function have been well-characterized, but its lifecycle is under active investigation. In this review, advances in studying the lifecycle of Photosystem II in cyanobacteria will be discussed, with a particular emphasis on new structural findings enabled by cryo-electron microscopy. These structural findings complement a rich and growing body of biochemical and molecular biology research into Photosystem II assembly and repair.

Keywords: Photosystem II; cryo-electron microscopy; cyanobacteria; oxygenic photosynthesis; photosynthetic reaction center.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
PSII monomer (PSII forms a dimer in vivo). Modules are colored as indicated.
Figure 2
Figure 2
PSII Lifecycle, simplified. Not all accessory assembly chaperones are illustrated. (A–D) illustrate de novo synthesis, while (D–G) illustrate the repair cycle. (A) The pre-D1 and pre-D2 complexes come together to form the RC module. (B) RC and pre-CP47 modules come together to form the RC47 complex. Psb28 binds at this stage. (C) Psb27-PSII forms from pre-CP43 module and RC47. (D) The active PSII monomer is formed in a series of steps, which include processing of the D1 C-terminus, photo-assembly of the Mn4CaO5 cluster, and binding of extrinsic proteins PsbO, PsbV, PsbU, and PsbQ. The active PSII dimer forms following complete monomer assembly. (E) Following a photodamage event, the extrinsic proteins dissociate, Psb27 binds, and the dimer dissociates into monomers. (F) Damaged subunits are removed and proteolytically degraded. (G) Newly synthesized PSII subunits are inserted into recycled subunits to form a Psb27-PSII complex and the repair pathway re-joins the de novo synthesis pathway.
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