Aggregates of the Chlorophyll-Binding Protein IsiA (CP43') Dissipate Energy in Cyanobacteria

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• 作者：Janne A. Ihalainen ; Sandrine D'Haene ; Nataliya Yeremenko ; Henny van Roon ; Ana A. Arteni ; Egbert J. Boekema ; Rienk van Grondelle ; Hans C. P. Matthijs ; and Jan P. Dekker
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：August 16, 2005
• 年：2005
• 卷：44
• 期：32
• 页码：10846 - 10853
• 全文大小：211K
• 年卷期：v.44,no.32(August 16, 2005)
• ISSN：1520-4995

文摘

In many natural habitats, growth of cyanobacteria may be limited by a low concentration ofiron. Cyanobacteria respond to this condition by expressing a number of iron-stress-inducible genes, ofwhich the isiA gene encodes a chlorophyll-binding protein known as IsiA or CP43'. IsiA monomersassemble into ring-shaped polymers that encircle trimeric or monomeric photosystem I (PSI), or are presentin supercomplexes without PSI, in particular upon prolonged iron starvation. In this report, we presentsteady-state and time-resolved fluorescence measurements of isolated IsiA aggregates that have been purifiedfrom an iron-starved psaFJ-minus mutant of Synechocystis PCC 6803. We show that these aggregateshave a fluorescence quantum yield of ~2% compared to that of chlorophyll a in acetone, and that thedominating fluorescence lifetimes are 66 and 210 ps, more than 1 order of magnitude shorter than that offree chlorophyll a. Comparison of the temperature dependence of the fluorescence yields and spectra ofthe isolated aggregates and of the cells from which they were obtained suggests that these aggregatesoccur naturally in the iron-starved cells. We suggest that IsiA aggregates protect cyanobacterial cellsagainst the deleterious effects of light.