title: Characterization of red-shifted phycobilisomes isolated from the chlorophyll f-containing cyanobacterium Halomicronema hongdechloris.
abstract: Phycobilisomes are the main light-harvesting protein complexes in cyanobacteria and some algae. It is commonly accepted that these complexes only absorb green and orange light, complementing chlorophyll absorbance. Here, we present a new phycobilisome derived complex that consists only of allophycocyanin core subunits, having red-shifted absorption peaks of 653 and 712 nm. These red-shifted phycobiliprotein complexes were isolated from the chlorophyll f-containing cyanobacterium, Halomicronema hongdechloris, grown under monochromatic 730 nm-wavelength (far-red) light. The 3D model obtained from single particle analysis reveals a double disk assembly of 120-145 Å with two α/β allophycocyanin trimers fitting into the two separated disks. They are significantly smaller than typical phycobilisomes formed from allophycocyanin subunits and core-membrane linker proteins, which fit well with a reduced distance between thylakoid membranes observed from cells grown under far-red light. Spectral analysis of the dissociated and denatured phycobiliprotein complexes grown under both these light conditions shows that the same bilin chromophore, phycocyanobilin, is exclusively used. Our findings show that red-shifted phycobilisomes are required for assisting efficient far-red light harvesting. Their discovery provides new insights into the molecular mechanisms of light harvesting under extreme conditions for photosynthesis, as well as the strategies involved in flexible chromatic acclimation to diverse light conditions.
authors.affiliation: ARC Centre of Excellence for Translational Photosynthesis and School of Biological Sciences, University of Sydney, NSW 2006, Australia.
authors.forename: Yaqiong
authors.initials: Y
authors.lastname: Li
authors.affiliation: ARC Centre of Excellence for Translational Photosynthesis and School of Biological Sciences, University of Sydney, NSW 2006, Australia.
authors.forename: Yuankui
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Australian Nuclear Science and Technology Organisation, Lucas Heights Campus, NSW 2234, Australia.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Garvey
authors.affiliation: Department of Biological Sciences, Macquarie University, NSW 2109, Australia.
authors.forename: Debra
authors.initials: D
authors.lastname: Birch
authors.affiliation: Applied Physical Chemistry, KTH Royal Institute of Technology, StockholmSE-100 44, Sweden.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Corkery
authors.affiliation: ARC Centre of Excellence for Translational Photosynthesis and School of Biological Sciences, University of Sydney, NSW 2006, Australia.
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Loughlin
authors.affiliation: Department of Biology I, University of Munich, Menzinger Str. 67, D-80638 München, Germany.
authors.forename: Hugo
authors.initials: H
authors.lastname: Scheer
authors.affiliation: Department of Chemistry and Biomolecular Sciences, Macquarie University, NSW 2109, Australia.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Willows
authors.affiliation: ARC Centre of Excellence for Translational Photosynthesis and School of Biological Sciences, University of Sydney, NSW 2006, Australia. Electronic address: min.chen@sydney.edu.au.
authors.forename: Min
authors.initials: M
authors.lastname: Chen
mesh_terms: D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000502:physiology; D000458:Cyanobacteria / Q000378:metabolism*; D010788:Photosynthesis; D045524:Phycobilisomes / Q000737:chemistry / Q000502:physiology*
chemical_list: D045524:Phycobilisomes; C583352:chlorophyll f; D002734:Chlorophyll
keywords: Complementary chromatic acclimation; Cyanobacteria; Far-red light; Photosynthesis; Phycobilisome; Small angle neutron scattering