Michel K P, Exss-Sonne P, Scholten-Beck G, Kahmann U, Ruppel H G, Pistorius E K
Morphologie der Pflanzen und Feinbau der Zelle, Universität Bielefeld, Germany.
Planta. 1998 May;205(1):73-81. doi: 10.1007/s004250050298.
Iron-deficiency-induced protein A (IdiA) with a calculated molecular mass of 35 kDa has previously been shown to be essential under manganese- and iron-limiting conditions in the cyanobacteria Synechococcus PCC 6301 and PCC 7942. Studies of mutants indicated that in the absence of IdiA mainly photosystem II becomes damaged, suggesting that the major function of IdiA is in Mn and not Fe metabolism (Michel et al. 1996, Microbiology 142: 2635-2645). To further elucidate the function of IdiA, the immunocytochemical localization of IdiA in the cell was examined. These investigations provided evidence that under mild Fe deficiency IdiA is intracellularly localized and is mainly associated with the thylakoid membrane in Synechococcus PCC 6301. The protein became distributed throughout the cell under severe Fe limitation when substantial morphological changes had already occurred. For additional verification of a preferential thylakoid membrane association of IdiA, these investigations were extended to the thermophilic Synechococcus elongatus. In this cyanobacterium Mn deficiency could be obtained more rapidly than in the mesophilic Synechococcus PCC 6301 and PCC 7942, and the thylakoid membrane structure proved to be more stable under limiting growth conditions. The immunocytochemical investigations with this cyanobacterium clearly supported a thylakoid membrane association of IdiA. In addition, evidence was obtained for a localization of IdiA on the cytoplasmic side of the thylakoid membrane. All available data support a function of IdiA as an Mn-binding protein that facilitates transport of Mn via the thylakoid membrane into the lumen to provide photosystem II with Mn. A possible explanation for the observation that IdiA was not only expressed under Mn deficiency but also under Fe deficiency is given in the discussion.
先前已表明，计算分子量为35 kDa的缺铁诱导蛋白A（IdiA）在蓝藻聚球藻PCC 6301和PCC 7942的锰和铁限制条件下至关重要。对突变体的研究表明，在缺乏IdiA的情况下，主要是光系统II受损，这表明IdiA的主要功能在于锰代谢而非铁代谢（Michel等人，1996年，《微生物学》142: 2635 - 2645）。为了进一步阐明IdiA的功能，研究了IdiA在细胞内的免疫细胞化学定位。这些研究提供了证据，表明在轻度缺铁条件下，IdiA定位于细胞内，并且在聚球藻PCC 6301中主要与类囊体膜相关。当已经发生大量形态变化时，在严重铁限制条件下，该蛋白分布于整个细胞。为了进一步验证IdiA与类囊体膜的优先结合，这些研究扩展到嗜热聚球藻。在这种蓝藻中，与嗜温聚球藻PCC 6301和PCC 7942相比，能更快地实现锰缺乏，并且在限制生长条件下类囊体膜结构被证明更稳定。对这种蓝藻的免疫细胞化学研究明确支持IdiA与类囊体膜的结合。此外，还获得了IdiA定位于类囊体膜细胞质侧的证据。所有现有数据支持IdiA作为一种锰结合蛋白的功能，它促进锰通过类囊体膜运输到腔内，为光系统II提供锰。讨论中给出了关于IdiA不仅在锰缺乏而且在铁缺乏条件下都表达这一现象的可能解释。
