title: MS-based cross-linking analysis reveals the location of the PsbQ protein in cyanobacterial photosystem II.
abstract: 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 (120)K of PsbQ and (180)K and (59)K of PsbO, and between (102)K of PsbQ and (440)D 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.
authors.affiliation: Departments of Biology and Chemistry, Washington University in St. Louis, St. Louis, MO 63130.
authors.forename: Haijun
authors.initials: H
authors.lastname: Liu
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Weisz
authors.forename: Ilan
authors.initials: I
authors.lastname: Vidavsky
authors.forename: Michael L
authors.initials: ML
authors.lastname: Gross
authors.forename: Himadri B
authors.initials: HB
authors.lastname: Pakrasi
mesh_terms: D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002853:Chromatography, Liquid; D003432:Cross-Linking Reagents / Q000737:chemistry; D008958:Models, Molecular; D009154:Mutation; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010802:Phylogeny; D046939:Synechocystis / Q000145:classification / Q000378:metabolism*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D045332:Photosystem II Protein Complex
keywords: photosystem II structure; protein cross-linking