Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 111, Issue 12, Pages 4638-4643Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1323063111
Keywords
photosystem II structure; protein cross-linking
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Funding
- US Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0001035]
- National Science Foundation [MCB0745611]
- National Institute of General Medical Sciences (National Institutes of Health) [8 P41 GM103422-35]
- Direct For Biological Sciences
- Div Of Molecular and Cellular Bioscience [0745611] Funding Source: National Science Foundation
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PsbQ is a luminal extrinsic protein component that regulates the water splitting activity of photosystem II (PSII) in plants, algae, and cyanobacteria. However, PsbQ is not observed in the currently available crystal structures of PSII from thermophilic cyanobacteria. The structural location of PsbQ within the PSII complex has therefore remained unknown. Here, we report chemical cross-linking followed by immunodetection and liquid chromatography/tandem MS analysis of a dimeric PSII complex isolated from the model cyanobacterium, Synechocystis sp. PCC 6803, to determine the binding site of PsbQ within PSII. Our results demonstrate that PsbQ is closely associated with the PsbO and CP47 proteins, as revealed by cross-links detected between K-120 of PsbQ and K-180 and K-59 of PsbO, and between K-102 of PsbQ and D-440 of CP47. We further show that genetic deletion of the psbO gene results in the complete absence of PsbQ in PSII complexes as well as the loss of the dimeric form of PSII. Overall, our data provide a molecular-level description of the enigmatic binding site of PsbQ in PSII in a cyanobacterium. These results also help us understand the sequential incorporation of the PsbQ protein during the PSII assembly process, as well as its stabilizing effect on the oxygen evolution activity of PSII.
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