title: The terminal phycobilisome emitter, LCM: A light-harvesting pigment with a phytochrome chromophore.
abstract: Photosynthesis relies on energy transfer from light-harvesting complexes to reaction centers. Phycobilisomes, the light-harvesting antennas in cyanobacteria and red algae, attach to the membrane via the multidomain core-membrane linker, L(CM). The chromophore domain of L(CM) forms a bottleneck for funneling the harvested energy either productively to reaction centers or, in case of light overload, to quenchers like orange carotenoid protein (OCP) that prevent photodamage. The crystal structure of the solubly modified chromophore domain from Nostoc sp. PCC7120 was resolved at 2.2 Å. Although its protein fold is similar to the protein folds of phycobiliproteins, the phycocyanobilin (PCB) chromophore adopts ZZZssa geometry, which is unknown among phycobiliproteins but characteristic for sensory photoreceptors (phytochromes and cyanobacteriochromes). However, chromophore photoisomerization is inhibited in L(CM) by tight packing. The ZZZssa geometry of the chromophore and π-π stacking with a neighboring Trp account for the functionally relevant extreme spectral red shift of L(CM). Exciton coupling is excluded by the large distance between two PCBs in a homodimer and by preservation of the spectral features in monomers. The structure also indicates a distinct flexibility that could be involved in quenching. The conclusions from the crystal structure are supported by femtosecond transient absorption spectra in solution.
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China; Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany;
authors.forename: Kun
authors.initials: K
authors.lastname: Tang
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China;
authors.forename: Wen-Long
authors.initials: WL
authors.lastname: Ding
authors.affiliation: X-Ray Facility and Crystal Farm, Heinrich-Heine-Universität, D-40225 Dusseldorf, Germany;
authors.forename: Astrid
authors.initials: A
authors.lastname: Höppner
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China;
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China;
authors.forename: Lun
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Biophysics Section, Department of Physics and Astronomy, Faculty of Sciences, VU University, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands;
authors.forename: Yusaku
authors.initials: Y
authors.lastname: Hontani
authors.affiliation: Biophysics Section, Department of Physics and Astronomy, Faculty of Sciences, VU University, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands;
authors.forename: John T M
authors.initials: JT
authors.lastname: Kennis
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, D-45470 Mülheim an der Ruhr, Germany;
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gärtner
authors.affiliation: Department Biologie I, Universität München, D-80638 Munich, Germany.
authors.forename: Hugo
authors.initials: H
authors.lastname: Scheer
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China;
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China; khzhao@163.com.
authors.forename: Kai-Hong
authors.initials: KH
authors.lastname: Zhao
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004735:Energy Transfer / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D009154:Mutation; D046937:Nostoc / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects; D052979:Phycobiliproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045524:Phycobilisomes / Q000378:metabolism*; D017510:Protein Folding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D052979:Phycobiliproteins; D045524:Phycobilisomes
keywords: core-membrane linker; crystal structure; cyanobacteria; photosynthesis; phycobilisome