title: Adapting photosynthesis to the near-infrared: non-covalent binding of phycocyanobilin provides an extreme spectral red-shift to phycobilisome core-membrane linker from Synechococcus sp. PCC7335.
abstract: Phycobiliproteins that bind bilins are organized as light-harvesting complexes, phycobilisomes, in cyanobacteria and red algae. The harvested light energy is funneled to reaction centers via two energy traps, allophycocyanin B and the core-membrane linker, ApcE1 (conventional ApcE). The covalently bound phycocyanobilin (PCB) of ApcE1 absorbs near 660 nm and fluoresces near 675 nm. In cyanobacteria capable of near infrared photoacclimation, such as Synechococcus sp. PCC7335, there exist even further spectrally red shifted components absorbing >700 nm and fluorescing >710 nm. We expressed the chromophore domain of the extra core-membrane linker from Synechococcus sp. PCC7335, ApcE2, in E. coli together with enzymes generating the chromophore, PCB. The resulting chromoproteins, PCB-ApcE2(1-273) and the more truncated PCB-ApcE2(24-245), absorb at 700 nm and fluoresce at 714 nm. The red shift of ~40 nm compared with canonical ApcE1 results from non-covalent binding of the chromophore by which its full conjugation length including the Δ3,3(1) double bond is preserved. The extreme spectral red-shift could not be ascribed to exciton coupling: dimeric PCB-ApcE2(1-273) and monomeric-ApcE2(24-245) absorbed and fluoresced similarly. Chromophorylation of ApcE2 with phycoerythrobilin- or phytochromobilin resulted in similar red shifts (absorption at 615 and 711 nm, fluorescence at 628 or 726 nm, respectively), compared to the covalently bound chromophores. The self-assembled non-covalent chromophorylation demonstrates a novel access to red and near-infrared emitting fluorophores. Brightly fluorescent biomarking was exemplified in E. coli by single-plasmid transformation.
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Dan
authors.initials: D
authors.lastname: Miao
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Wen-Long
authors.initials: WL
authors.lastname: Ding
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Bao-Qing
authors.initials: BQ
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Lu
authors.initials: L
authors.lastname: Lu
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Qian-Zhao
authors.initials: QZ
authors.lastname: Xu
authors.affiliation: Dept. Biologie 1-Botanik, Universität München, 80638 München, Germany.
authors.forename: Hugo
authors.initials: H
authors.lastname: Scheer
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China. Electronic address: khzhao@163.com.
authors.forename: Kai-Hong
authors.initials: KH
authors.lastname: Zhao
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D010788:Photosynthesis; D052980:Phycobilins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045524:Phycobilisomes / Q000378:metabolism*; D010798:Phycocyanin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010799:Phycoerythrin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D052980:Phycobilins; D045524:Phycobilisomes; D011994:Recombinant Proteins; C504557:allophycocyanin B; D010798:Phycocyanin; D010799:Phycoerythrin; C011070:phycoerythrobilin; C011069:phycocyanobilin
keywords: Core-membrane linker; Cyanobacteria; Fluorescence biolabel; Phycobilisome; Phycocyanobilin; Phycoerythrobilin; Phytochromobilin; Spectral tuning