Lehrstuhl für Molekulare Zellphysiologie, Fakultät für Biologie, Universität Bielefeld, Universitätsstraße 25, 33615, Bielefeld, Germany.
Photosynth Res. 2011 Sep;108(2-3):121-32. doi: 10.1007/s11120-011-9661-1. Epub 2011 May 24.
Iron limitation has a strong impact on electron transport reactions of the unicellular fresh water cyanobacterium Synechococcus elongatus PCC 7942 (thereafter referred to as S. elongatus). Among the various adaptational processes on different cellular levels, iron limitation induces a strongly enhanced expression of IdiC (iron-deficiency-induced protein C). In this article, we show that IdiC is loosely attached to the thylakoid and to the cytoplasmic membranes and that its expression is enhanced during conditions of iron starvation and during the late growth phase. The intracellular IdiC level was even more increased when additional iron was replenished in the late growth phase. On the basis of its amino acid sequence and of its absorbance spectrum, IdiC can be classified as a member of the family of thioredoxin (TRX)-like (2Fe-2S) ferredoxins. The presence of an iron cofactor in IdiC was detected by inductive coupled plasma optical emission spectrometry (ICP-OES). Comparative measurements of electron transport activities of S. elongatus wild type (WT) and an IdiC-merodiploid mutant called MuD, which contained a strongly reduced IdiC content under iron-sufficient as well as iron-deficient growth conditions, were performed. The results revealed that MuD had a strongly increased light sensitivity, especially under iron limitation. The measurements of photosystem II (PS II)-mediated electron transport rates in WT and MuD strain showed that PS II activity was significantly lower in MuD than in the WT strain. Moreover, P(700) (+) re-reduction rates provided evidence that the respiratory activities, which were very low in the MuD strain in the presence of iron, significantly increased in iron-starved cells. Thus, an increase in respiration may compensate for the drastic decrease of photosynthetic electron transport activity in MuD grown under iron starvation. Based on the similarity of the S. elongatus IdiC to the NuoE subunit of the NDH-1 complex in Escherichia coli, it is likely that IdiC has a function in the electron transport processes from NAD(P)H to the plastoquinone pool. This is in agreement with the up-regulation of IdiC in the late growth phase as well as under stress conditions when PS II is damaged. As absence or high reduction of the IdiC level would prevent or reduce the formation of functional NDH-1 complexes, under such conditions electron transport routes via alternative substrate dehydrogenases, donating electrons to the plastoquinone pool, can be assumed to be up-regulated.
铁限制对单细胞淡水蓝藻集胞藻 PCC 7942（以下简称 S. elongatus）的电子传递反应有强烈影响。在不同细胞水平的各种适应过程中，铁限制诱导 IdiC（缺铁诱导蛋白 C）的强烈表达。在本文中，我们表明 IdiC 松散地附着于类囊体和细胞质膜上，并且在铁饥饿和生长后期表达增强。在生长后期补充额外的铁时，细胞内 IdiC 水平甚至进一步增加。根据其氨基酸序列和吸收光谱，IdiC 可归类为硫氧还蛋白 (TRX)-样 (2Fe-2S) 铁氧还蛋白家族的成员。通过感应耦合等离子体发射光谱法 (ICP-OES) 检测到 IdiC 中的铁辅因子。对 S. elongatus 野生型 (WT) 和一种称为 MuD 的 IdiC 部分二倍体突变体的电子传递活性进行了比较测量，该突变体在铁充足和缺铁生长条件下都含有强烈降低的 IdiC 含量。结果表明，MuD 在光下的敏感性明显增强，尤其是在缺铁条件下。在 WT 和 MuD 菌株中测量光系统 II (PS II)-介导的电子传递速率表明，PS II 活性在 MuD 中明显低于 WT 菌株。此外，P(700) (+) 再还原速率表明，在 MuD 菌株中，呼吸活性在铁存在下非常低，但在缺铁细胞中显著增加。因此，呼吸作用的增加可能补偿了 MuD 在缺铁条件下生长时光合作用电子传递活性的急剧下降。基于 S. elongatus IdiC 与大肠杆菌 NDH-1 复合物的 NuoE 亚基的相似性，IdiC 很可能在 NAD(P)H 到质醌库的电子传递过程中具有功能。这与 IdiC 在生长后期以及 PS II 受损的应激条件下的上调一致。由于 IdiC 水平的缺失或高度还原会阻止或减少功能性 NDH-1 复合物的形成，因此可以假设在这种情况下，通过替代底物脱氢酶将电子传递到质醌库的电子传递途径被上调。
