title: The cyanobacterial cytochrome b6f subunit PetP adopts an SH3 fold in solution.
abstract: PetP is a peripheral subunit of the cytochrome b(6)f complex (b(6)f) present in both, cyanobacteria and red algae. It is bound to the cytoplasmic surface of this membrane protein complex where it greatly affects the efficiency of the linear photosynthetic electron flow although it is not directly involved in the electron transfer reactions. Despite the crystal structures of the b(6)f core complex, structural information for the transient regulatory b(6)f subunits is still missing. Here we present the first structure of PetP at atomic resolution as determined by solution NMR. The protein adopts an SH3 fold, which is a common protein motif in eukaryotes but comparatively rare in prokaryotes. The structure of PetP enabled the identification of the potential interaction site for b(6)f binding by conservation mapping. The interaction surface is mainly formed by two large loop regions and one short 310 helix which also exhibit an increased flexibility as indicated by heteronuclear steady-state {(1)H}-(15)N NOE and random coil index parameters. The properties of this potential b(6)f binding site greatly differ from the canonical peptide binding site which is highly conserved in eukaryotic SH3 domains. Interestingly, three other proteins of the photosynthetic electron transport chain share this SH3 fold with PetP: NdhS of the photosynthetic NADH dehydrogenase-like complex (NDH-1), PsaE of the photosystem 1 and subunit α of the ferredoxin-thioredoxin reductase have, similar to PetP, a great impact on the photosynthetic electron transport. Finally, a model is presented to illustrate how SH3 domains modulate the photosynthetic electron transport processes in cyanobacteria.
authors.affiliation: Plant Biochemistry, Faculty of Biology & Biotechnology, Ruhr University Bochum, Bochum, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Veit
authors.affiliation: Graduate School of Medical Life Science, Yokohama City University, Yokohama, Japan.
authors.forename: Aritaka
authors.initials: A
authors.lastname: Nagadoi
authors.affiliation: Plant Biochemistry, Faculty of Biology & Biotechnology, Ruhr University Bochum, Bochum, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Rögner
authors.affiliation: Plant Biochemistry, Faculty of Biology & Biotechnology, Ruhr University Bochum, Bochum, Germany. Electronic address: sascha.rexroth@ruhr-uni-bochum.de.
authors.forename: Sascha
authors.initials: S
authors.lastname: Rexroth
authors.affiliation: Biomolecular Spectroscopy, Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Bochum, Germany. Electronic address: raphael.stoll@ruhr-uni-bochum.de.
authors.forename: Raphael
authors.initials: R
authors.lastname: Stoll
authors.affiliation: Graduate School of Medical Life Science, Yokohama City University, Yokohama, Japan. Electronic address: ikegamit@yokohama-cu.ac.jp.
authors.forename: Takahisa
authors.initials: T
authors.lastname: Ikegami
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism; D045346:Cytochrome b6f Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004579:Electron Transport; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010788:Photosynthesis; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012996:Solutions / Q000737:chemistry*; D018909:src Homology Domains
chemical_list: D001426:Bacterial Proteins; D012996:Solutions; D045346:Cytochrome b6f Complex
keywords: Cytochrome b(6)f complex; Electron transport; PetP; Photosynthesis; SH3 domain; Thermosynechococcus elongatus