title: Far-red light photoacclimation: Chromophorylation of FR induced α- and β-subunits of allophycocyanin from Chroococcidiopsis thermalis sp. PCC7203.
abstract: Cyanobacterial light-harvesting complexes, phycobilisomes, can undergo extensive remodeling under varying light conditions. Acclimation to far-red light involves not only generation of red-shifted chlorophylls in the photosystems, but also induction of additional copies of core biliproteins that have been related to red-shifted components of the phycobilisome (Gan et al., Life 5, 4, 2015). We are studying the molecular basis for these acclimations in Chroococcidiopsis thermalis sp. PCC7203. Five far-red induced allophycocyanin subunits (ApcA2, ApcA3, ApcB2, ApcB3 and ApcF2) were expressed in Escherichia coli, together with S-type chromophore-protein lyases and in situ generated chromophore, phycocyanobilin. Only one subunit, ApcF2, shows an unusual red-shift (λAmax~675nm, λFmax~698nm): it binds the chromophore non-covalently, thereby preserving its full conjugation length. This mechanism operates also in two Cys-variants of the induced subunits of bulky APC. All other wild-type subunits bind phycocyanobilin covalently to the conventional Cys-81 under catalysis of the lyase, CpcS1. Although three of them also show binding to additional cysteines, all absorb and fluoresce similar to conventional APC subunits (λAmax~610nm, λFmax~640nm). Another origin of red-shifted complexes was identified, however, when different wild-type α- and β-subunits of the far-red induced bulky APC were combined in a combinatorial fashion. Strongly red-shifted complexes (λFmax≤722nm) were formed when the α-subunit, PCB-ApcA2, and the β-subunit, PCB-ApcB2, were generated together in E. coli. This extreme aggregation-induced red-shift of ~90nm of covalently bound chromophores is reminiscent, but much larger, than the ~30nm observed with conventional APC.
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: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Jia-Xin
authors.initials: JX
authors.lastname: Han
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Qi-Ying
authors.initials: QY
authors.lastname: Tang
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: Dan
authors.initials: D
authors.lastname: Miao
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
authors.affiliation: Department Biologie I, Universität München, Menzinger Str. 67, D-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: D000222:Adaptation, Physiological; D001665:Binding Sites; D000458:Cyanobacteria / Q000737:chemistry*; D005453:Fluorescence; D008027:Light; D010798:Phycocyanin / Q000737:chemistry*; D021122:Protein Subunits
chemical_list: D021122:Protein Subunits; C002497:allophycocyanin; D010798:Phycocyanin
keywords: Allophycocyanin; Chromophorylation; Cyanobacteria; Energy transfer; Far-red photoacclimation; Phycobilisome; Phycocyanobilin