Department of Chemistry, Texas A&M University, College Station, Texas 77843.
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208.
J Biol Chem. 2019 Jan 4;294(1):50-62. doi: 10.1074/jbc.RA118.005233. Epub 2018 Oct 18.
Iron is critical for virtually all organisms, yet major questions remain regarding the systems-level understanding of iron in whole cells. Here, we obtained Mössbauer and EPR spectra of cells prepared under different nutrient iron concentrations, carbon sources, growth phases, and O concentrations to better understand their global iron content. We investigated WT cells and those lacking Fur, FtnA, Bfr, and Dps proteins. The coarse-grain iron content of exponentially growing cells consisted of iron-sulfur clusters, variable amounts of nonheme high-spin Fe species, and an unassigned residual quadrupole doublet. The iron in stationary-phase cells was dominated by magnetically ordered Fe ions due to oxyhydroxide nanoparticles. Analysis of cytosolic extracts by size-exclusion chromatography detected by an online inductively coupled plasma mass spectrometer revealed a low-molecular-mass (LMM) Fe pool consisting of two iron complexes with masses of ∼500 (major) and ∼1300 (minor) Da. They appeared to be high-spin Fe species with mostly oxygen donor ligands, perhaps a few nitrogen donors, and probably no sulfur donors. Surprisingly, the iron content of and its reactivity with O were remarkably similar to those of mitochondria. In both cases, a "respiratory shield" composed of membrane-bound iron-rich respiratory complexes may protect the LMM Fe pool from reacting with O When exponentially growing cells transition to stationary phase, the shield deactivates as metabolic activity declines. Given the universality of oxidative phosphorylation in aerobic biology, the iron content and respiratory shield in other aerobic prokaryotes might be similar to those of and mitochondria.
铁对于几乎所有生物体都是至关重要的，但对于整个细胞中铁的系统水平理解仍存在重大问题。在这里，我们获得了在不同营养铁浓度、碳源、生长阶段和 O 浓度下制备的细胞的穆斯堡尔和 EPR 光谱，以更好地了解它们的整体铁含量。我们研究了 WT 细胞和缺乏 Fur、FtnA、Bfr 和 Dps 蛋白的细胞。指数生长期细胞的粗粒铁含量由铁硫簇、数量不定的非血红素高自旋 Fe 物种和未分配的剩余四极子双峰组成。由于水铁矿纳米颗粒，静止期细胞中的铁主要由磁有序的 Fe 离子组成。通过在线电感耦合等离子体质谱仪检测的大小排阻色谱法分析细胞溶质提取物揭示了一个低分子量（LMM）Fe 池，由两个铁复合物组成，分子量分别为约 500（主要）和约 1300（次要）Da。它们似乎是高自旋 Fe 物种，主要具有氧供体配体，可能有几个氮供体，可能没有硫供体。令人惊讶的是，的铁含量及其与 O 的反应性与线粒体非常相似。在这两种情况下，由膜结合的富含铁的呼吸复合物组成的“呼吸盾牌”可能会保护 LMM Fe 池免受与 O 的反应。当指数生长期细胞过渡到静止期时，随着代谢活性的下降，盾牌失活。鉴于需氧生物中氧化磷酸化的普遍性，其他需氧原核生物中的铁含量和呼吸盾牌可能与和线粒体相似。
