title: Mass spectrometry-based cross-linking study shows that the Psb28 protein binds to cytochromeb559in Photosystem II.
abstract: Photosystem II (PSII), a large pigment protein complex, undergoes rapid turnover under natural conditions. During assembly of PSII, oxidative damage to vulnerable assembly intermediate complexes must be prevented. Psb28, the only cytoplasmic extrinsic protein in PSII, protects the RC47 assembly intermediate of PSII and assists its efficient conversion into functional PSII. Its role is particularly important under stress conditions when PSII damage occurs frequently. Psb28 is not found, however, in any PSII crystal structure, and its structural location has remained unknown. In this study, we used chemical cross-linking combined with mass spectrometry to capture the transient interaction of Psb28 with PSII. We detected three cross-links between Psb28 and the α- and β-subunits of cytochromeb559, an essential component of the PSII reaction-center complex. These distance restraints enable us to position Psb28 on the cytosolic surface of PSII directly above cytochromeb559, in close proximity to the QBsite. Protein-protein docking results also support Psb28 binding in this region. Determination of the Psb28 binding site and other biochemical evidence allow us to propose a mechanism by which Psb28 exerts its protective effect on the RC47 intermediate. This study also shows that isotope-encoded cross-linking with the "mass tags" selection criteria allows confident identification of more cross-linked peptides in PSII than has been previously reported. This approach thus holds promise to identify other transient protein-protein interactions in membrane protein complexes.
authors.affiliation: Department of Biology, Washington University, St. Louis, MO 63130.|Department of Chemistry, Washington University, St. Louis, MO 63130.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Weisz
authors.affiliation: Department of Biology, Washington University, St. Louis, MO 63130.
authors.forename: Haijun
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Washington University, St. Louis, MO 63130.
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Biochemistry, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
authors.forename: Sundarapandian
authors.initials: S
authors.lastname: Thangapandian
authors.affiliation: Department of Biochemistry, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
authors.forename: Emad
authors.identifier: 0000-0001-8434-1010
authors.initials: E
authors.lastname: Tajkhorshid
authors.affiliation: Department of Chemistry, Washington University, St. Louis, MO 63130; pakrasi@wustl.edu mgross@wustl.edu.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Gross
authors.affiliation: Department of Biology, Washington University, St. Louis, MO 63130; pakrasi@wustl.edu mgross@wustl.edu.
authors.forename: Himadri B
authors.initials: HB
authors.lastname: Pakrasi
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003573:Cytochrome b Group / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005822:Genetic Vectors / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry; D062105:Molecular Docking Simulation; D010788:Photosynthesis / Q000235:genetics; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D054730:Protein Interaction Domains and Motifs; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013388:Succinimides / Q000737:chemistry*; D046939:Synechocystis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D003573:Cytochrome b Group; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins; D013388:Succinimides; C019313:cytochrome b559; C035760:bis(sulfosuccinimidyl)suberate
keywords: Photosystem II; chemical cross-linking; cyanobacteria; membrane protein; photosynthesis