Ihalainen Janne A, D'Haene Sandrine, Yeremenko Nataliya, van Roon Henny, Arteni Ana A, Boekema Egbert J, van Grondelle Rienk, Matthijs Hans C P, Dekker Jan P
Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Biochemistry. 2005 Aug 16;44(32):10846-53. doi: 10.1021/bi0510680.
In many natural habitats, growth of cyanobacteria may be limited by a low concentration of iron. Cyanobacteria respond to this condition by expressing a number of iron-stress-inducible genes, of which the isiA gene encodes a chlorophyll-binding protein known as IsiA or CP43'. IsiA monomers assemble into ring-shaped polymers that encircle trimeric or monomeric photosystem I (PSI), or are present in supercomplexes without PSI, in particular upon prolonged iron starvation. In this report, we present steady-state and time-resolved fluorescence measurements of isolated IsiA aggregates that have been purified from an iron-starved psaFJ-minus mutant of Synechocystis PCC 6803. We show that these aggregates have a fluorescence quantum yield of approximately 2% compared to that of chlorophyll a in acetone, and that the dominating fluorescence lifetimes are 66 and 210 ps, more than 1 order of magnitude shorter than that of free chlorophyll a. Comparison of the temperature dependence of the fluorescence yields and spectra of the isolated aggregates and of the cells from which they were obtained suggests that these aggregates occur naturally in the iron-starved cells. We suggest that IsiA aggregates protect cyanobacterial cells against the deleterious effects of light.
在许多自然栖息地中，蓝细菌的生长可能会受到低铁浓度的限制。蓝细菌通过表达一些铁应激诱导基因来应对这种情况，其中isiA基因编码一种称为IsiA或CP43'的叶绿素结合蛋白。IsiA单体组装成环形聚合物，环绕三聚体或单体光系统I（PSI），或者存在于没有PSI的超复合物中，特别是在长期铁饥饿时。在本报告中，我们展示了从集胞藻PCC 6803的铁饥饿psaFJ缺失突变体中纯化得到的分离的IsiA聚集体的稳态和时间分辨荧光测量结果。我们表明，与丙酮中的叶绿素a相比，这些聚集体的荧光量子产率约为2%，并且主要的荧光寿命为66和210皮秒，比游离叶绿素a的荧光寿命短超过1个数量级。对分离的聚集体及其来源细胞的荧光产率和光谱的温度依赖性进行比较表明，这些聚集体天然存在于铁饥饿的细胞中。我们认为IsiA聚集体可保护蓝细菌细胞免受光的有害影响。
