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Cryo-EM structure of a plant photosystem II supercomplex with light-harvesting protein Lhcb8 and & alpha;-tocopherol

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NATURE PLANTS
卷 9, 期 8, 页码 1359-+

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NATURE PORTFOLIO
DOI: 10.1038/s41477-023-01483-0

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This study presents the structure of photosystem II supercomplex from Picea abies determined by cryo-electron microscopy, revealing the presence of unique features such as the light-harvesting protein Lhcb8 and α-tocopherol molecule with potential physiological function.
The study presents the structure of photosystem II supercomplex from Picea abies solved by cryo-electron microscopy and describes its unique features-the presence of light-harvesting protein Lhcb8 and an & alpha;-tocopherol molecule with potential physiological function. The heart of oxygenic photosynthesis is the water-splitting photosystem II (PSII), which forms supercomplexes with a variable amount of peripheral trimeric light-harvesting complexes (LHCII). Our knowledge of the structure of green plant PSII supercomplex is based on findings obtained from several representatives of green algae and flowering plants; however, data from a non-flowering plant are currently missing. Here we report a cryo-electron microscopy structure of PSII supercomplex from spruce, a representative of non-flowering land plants, at 2.8 & ANGS; resolution. Compared with flowering plants, PSII supercomplex in spruce contains an additional Ycf12 subunit, Lhcb4 protein is replaced by Lhcb8, and trimeric LHCII is present as a homotrimer of Lhcb1. Unexpectedly, we have found & alpha;-tocopherol (& alpha;-Toc)/& alpha;-tocopherolquinone (& alpha;-TQ) at the boundary between the LHCII trimer and the inner antenna CP43. The molecule of & alpha;-Toc/& alpha;-TQ is located close to chlorophyll a614 of one of the Lhcb1 proteins and its chromanol/quinone head is exposed to the thylakoid lumen. The position of & alpha;-Toc in PSII supercomplex makes it an ideal candidate for the sensor of excessive light, as & alpha;-Toc can be oxidized to & alpha;-TQ by high-light-induced singlet oxygen at low lumenal pH. The molecule of & alpha;-TQ appears to shift slightly into the PSII supercomplex, which could trigger important structure-functional modifications in PSII supercomplex. Inspection of the previously reported cryo-electron microscopy maps of PSII supercomplexes indicates that & alpha;-Toc/& alpha;-TQ can be present at the same site also in PSII supercomplexes from flowering plants, but its identification in the previous studies has been hindered by insufficient resolution.

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