title: The identification of IsiA proteins binding chlorophyll d in the cyanobacterium Acaryochloris marina.
abstract: The bioavailable iron in many aquatic ecosystems is extremely low, and limits the growth and photosynthetic activity of phytoplankton. In response to iron limitation, a group of chlorophyll-binding proteins known as iron stress-induced proteins are induced and serve as accessory light-harvesting components for photosystems under iron limitation. In the present study, we investigated physiological features of Acaryochloris marina in response to iron-deficient conditions. The growth doubling time under iron-deficient conditions was prolonged to ~3.4 days compared with 1.9 days under normal culture conditions, accompanied with dramatically decreased chlorophyll content. The isolation of chlorophyll-binding protein complexes using sucrose density gradient centrifugation shows six main green bands and three main fluorescence components of 712, 728, and 748 nm from the iron-deficient culture. The fluorescence components of 712 and 728 nm co-exist in the samples collected from iron-deficient and iron-replete cultures and are attributed to Chl d-binding accessory chlorophyll-binding antenna proteins and also from photosystem II. A new chlorophyll-binding protein complex with its main fluorescence peak at 748 nm was observed and enriched in the heaviest fraction from the samples collected from the iron-deficient culture only. Combining western blotting analysis using antibodies of CP47 (PSII), PsaC (PSI) and IsiA and proteomic analysis on an excised protein band at ~37 kDa, the heaviest fraction (-F6) isolated from iron-deficient culture contained Chl d-bound PSI-IsiA supercomplexes. The PSII-antenna supercomplexes isolated from iron-replete conditions showed two fluorescence peaks of 712 and 728 nm, which can be assigned as 6-transmembrane helix chlorophyll-binding antenna and photosystem II fluorescence, respectively, which is supported by protein analysis of the fractions (F5 and F6).
authors.affiliation: School of Life Sciences, and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, 430079, Hubei, People's Republic of China.
authors.forename: Zheng-Ke
authors.initials: ZK
authors.lastname: Li
authors.affiliation: School of Life Sciences, and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, 430079, Hubei, People's Republic of China.
authors.forename: Yan-Chao
authors.initials: YC
authors.lastname: Yin
authors.affiliation: School of Life Sciences, and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, 430079, Hubei, People's Republic of China.
authors.forename: Lu-Dan
authors.initials: LD
authors.lastname: Zhang
authors.affiliation: School of Life Sciences, and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, 430079, Hubei, People's Republic of China.
authors.forename: Zhong-Chun
authors.initials: ZC
authors.lastname: Zhang
authors.affiliation: School of Life Sciences, and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, 430079, Hubei, People's Republic of China.
authors.forename: Guo-Zheng
authors.initials: GZ
authors.lastname: Dai
authors.affiliation: School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, 2006, Australia. min.chen@sydney.edu.au.
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.affiliation: School of Life Sciences, and Hubei Key Laboratory of Genetic Regulation and Integrative Biology, Central China Normal University, Wuhan, 430079, Hubei, People's Republic of China. bsqiu@mail.ccnu.edu.cn.
authors.forename: Bao-Sheng
authors.initials: BS
authors.lastname: Qiu
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism*; D061146:Chlorophyll Binding Proteins / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D007501:Iron / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013696:Temperature; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; D061146:Chlorophyll Binding Proteins; D046912:Multiprotein Complexes; D002734:Chlorophyll; C107509:chlorophyll d; D007501:Iron
keywords: Acaryochloris marina; Accessory chlorophyll-binding proteins (CBPs); Iron limitation; Iron-stress-induced protein A (IsiA); Photosynthesis; Six transmembrane helix family of chlorophyll-binding proteins/antenna