A Novel Prokaryote-Type ECF/ABC Transporter Module in Chloroplast Metal Homeostasis
A Novel Prokaryote-Type ECF/ABC Transporter Module in Chloroplast Metal Homeostasis
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DOI：
10.3389/fpls.2019.01264
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发表时间：
2019-10
影响因子：
5.6
通讯作者：
L. Voith von Voithenberg;Jiyoung Park;Roland Stübe;C. Lux;Youngsook Lee;K. Philippar
中科院分区：
文献类型：
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作者：
L. Voith von Voithenberg;Jiyoung Park;Roland Stübe;C. Lux;Youngsook Lee;K. Philippar
在进化过程中，叶绿体被确立为光合作用的场所，叶绿体是由今天蓝藻的原核祖先与真核宿主细胞内共生而来的。因此，叶绿体细胞器中含有铁、铜和锰等过渡金属，它们的氧化还原能力对光合作用的电子传递是必不可少的。尽管叶绿体中金属离子的运输、储存和辅因子组装在整个植物生长发育过程中受到严格的控制和至关重要，但对叶绿体金属运输蛋白的分子性质的了解仍然是零散的。在此，我们鉴定了拟南芥中可溶的、与ATP结合的ABC转运蛋白亚基ABCI10和ABCI11，它们与原核生物的多亚单位ABC转运蛋白的组成相似。ABCI10和ABCI11蛋白似乎都强烈地附着在叶绿体固有膜上，很可能是ABCI10的内膜，也可能是ABCI11的质球蛋白。在拟南芥中ABCI10和ABCI11基因产物的缺失导致极度矮化、白化的植物表现出叶绿体生物合成受损和金属动态平衡失调。进一步，我们确定膜内固有蛋白ABCI12是ABCI10在内膜中潜在的相互作用伙伴。我们的结果表明，ABCI12插入到叶绿体内被膜中，很可能含有5个预测的α-螺旋跨膜结构域，代表了原核型能量偶联因子ABC-转运蛋白复合体的膜内亚基。在细菌中，这些多亚单位ECF进口体广泛分布，用于吸收镍和钴金属离子，以及进口维生素和其他几种代谢物。因此，我们认为ABCI10(作为ATPase A亚基)和ABCI12(作为膜固有的、能量耦合的T亚基)是原核型ECF转运体的一个新的、叶绿体被膜定位的AAT能量耦合模块的一部分，最有可能参与金属离子的吸收。
During evolution, chloroplasts, which originated by endosymbiosis of a prokaryotic ancestor of today’s cyanobacteria with a eukaryotic host cell, were established as the site for photosynthesis. Therefore, chloroplast organelles are loaded with transition metals including iron, copper, and manganese, which are essential for photosynthetic electron transport due to their redox capacity. Although transport, storage, and cofactor-assembly of metal ions in chloroplasts are tightly controlled and crucial throughout plant growth and development, knowledge on the molecular nature of chloroplast metal-transport proteins is still fragmentary. Here, we characterized the soluble, ATP-binding ABC-transporter subunits ABCI10 and ABCI11 in Arabidopsis thaliana, which show similarities to components of prokaryotic, multisubunit ABC transporters. Both ABCI10 and ABCI11 proteins appear to be strongly attached to chloroplast-intrinsic membranes, most likely inner envelopes for ABCI10 and possibly plastoglobuli for ABCI11. Loss of ABCI10 and ABCI11 gene products in Arabidopsis leads to extremely dwarfed, albino plants showing impaired chloroplast biogenesis and deregulated metal homeostasis. Further, we identified the membrane-intrinsic protein ABCI12 as potential interaction partner for ABCI10 in the inner envelope. Our results suggest that ABCI12 inserts into the chloroplast inner envelope membrane most likely with five predicted α-helical transmembrane domains and represents the membrane-intrinsic subunit of a prokaryotic-type, energy-coupling factor (ECF) ABC-transporter complex. In bacteria, these multisubunit ECF importers are widely distributed for the uptake of nickel and cobalt metal ions as well as for import of vitamins and several other metabolites. Therefore, we propose that ABCI10 (as the ATPase A-subunit) and ABCI12 (as the membrane-intrinsic, energy-coupling T-subunit) are part of a novel, chloroplast envelope-localized, AAT energy-coupling module of a prokaryotic-type ECF transporter, most likely involved in metal ion uptake.