Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 116, Issue 35, Pages 17316-17322Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1906726116
Keywords
diatom; photosystem II; cryo-electron tomography; thylakoid membranes; functional absorption analysis
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Funding
- National Institute of Health Midwest Consortium for High Resolution Cryo-electron Microscopy [U24 GM116789-01A1]
- National Science Foundation EAGER award [1558128]
- National Institute of Health [R01GM080139, P01GM121203]
- Rutgers Busch Biomedical Research Grant
- Bennett L. Smith Endowment
- China Scholarship Council [201606375128]
- Div Of Molecular and Cellular Bioscience
- Direct For Biological Sciences [1558128] Funding Source: National Science Foundation
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A descendant of the red algal lineage, diatoms are unicellular eukaryotic algae characterized by thylakoid membranes that lack the spatial differentiation of stroma and grana stacks found in green algae and higher plants. While the photophysiology of diatoms has been studied extensively, very little is known about the spatial organization of the multimeric photosynthetic protein complexes within their thylakoid membranes. Here, using cryoelectron tomography, proteomics, and biophysical analyses, we elucidate the macromolecular composition, architecture, and spatial distribution of photosystem II complexes in diatom thylakoid membranes. Structural analyses reveal 2 distinct photosystem II populations: loose clusters of complexes associated with antenna proteins and compact 2D crystalline arrays of dimeric cores. Biophysical measurements reveal only 1 photosystem II functional absorption cross section, suggesting that only the former population is photosynthetically active. The tomographic data indicate that the arrays of photosystem II cores are physically separated from those associated with antenna proteins. We hypothesize that the islands of photosystem cores are repair stations, where photodamaged proteins can be replaced. Our results strongly imply convergent evolution between the red and the green photosynthetic lineages toward spatial segregation of dynamic, functional microdomains of photosystem II supercomplexes.
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