Bibby T S, Nield J, Barber J
Wolfson Laboratories, Department of Biological Sciences, Imperial College of Science, Technology & Medicine, London, UK.
Nature. 2001 Aug 16;412(6848):743-5. doi: 10.1038/35089098.
Although iron is the fourth most abundant element in the Earth's crust, its concentration in the aquatic ecosystems-particularly the open oceans-is sufficiently low to limit photosynthetic activity and phytoplankton growth. Cyanobacteria, a major class of phytoplankton, respond to iron deficiency by expressing the 'iron-stress-induced' gene, isiA(ref. 3). The protein encoded by this gene has an amino-acid sequence that shows significant homology with one of the chlorophyll a-binding proteins (CP43) of photosystem II (PSII). The precise function of the CP43-like protein, here called CP43', has not been elucidated, although there have been many suggestions. Here we show that CP43' associates with photosystem I (PSI) to form a complex that consists of a ring of 18 CP43' molecules around a PSI trimer. This significantly increases the size of the light-harvesting system of PSI. The utilization of a PSII-like protein as an extra antenna for PSI emphasises the flexibility of cyanobacterial light-harvesting systems, and seems to be a strategy which compensates for the lowering of phycobilisome and PSI levels in response to iron deficiency.
尽管铁是地壳中含量第四丰富的元素，但其在水生生态系统（尤其是公海）中的浓度足够低，足以限制光合作用和浮游植物的生长。蓝细菌是浮游植物的主要类别，通过表达“铁应激诱导”基因isiA（参考文献3）来应对铁缺乏。该基因编码的蛋白质具有与光系统II（PSII）的叶绿素a结合蛋白之一（CP43）显著同源的氨基酸序列。尽管有许多推测，但这种类似CP43的蛋白质（此处称为“CP43'”）的确切功能尚未阐明。在此我们表明，CP43'与光系统I（PSI）结合形成一个复合物，该复合物由围绕PSI三聚体的18个CP43'分子环组成。这显著增加了PSI的光捕获系统的大小。利用类似PSII的蛋白质作为PSI的额外天线，强调了蓝细菌光捕获系统的灵活性，并且似乎是一种补偿因铁缺乏而导致的藻胆体和PSI水平降低的策略。
