Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.
Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, USA.
Nat Commun. 2017 Jul 20;8:16110. doi: 10.1038/ncomms16110.
Iron-sulfur clusters are ubiquitous in biology and function in electron transfer and catalysis. They are assembled from iron and cysteine sulfur on protein scaffolds. Iron is typically stored as iron oxyhydroxide, ferrihydrite, encapsulated in 12 nm shells of ferritin, which buffers cellular iron availability. Here we have characterized IssA, a protein that stores iron and sulfur as thioferrate, an inorganic anionic polymer previously unknown in biology. IssA forms nanoparticles reaching 300 nm in diameter and is the largest natural metalloprotein complex known. It is a member of a widely distributed protein family that includes nitrogenase maturation factors, NifB and NifX. IssA nanoparticles are visible by electron microscopy as electron-dense bodies in the cytoplasm. Purified nanoparticles appear to be generated from 20 nm units containing ∼6,400 Fe atoms and ∼170 IssA monomers. In support of roles in both iron-sulfur storage and cluster biosynthesis, IssA reconstitutes the [4Fe-4S] cluster in ferredoxin in vitro.
铁硫簇在生物学中无处不在，它们在电子传递和催化中发挥作用。它们由铁和半胱氨酸硫在蛋白质支架上组装而成。铁通常以铁氧氢氧化物、水铁矿的形式储存，被包裹在铁蛋白的 12nm 壳中，从而缓冲细胞内铁的可用性。在这里，我们描述了 IssA 蛋白，它将铁和硫储存为硫代铁酸盐，这是一种以前在生物学中未知的无机阴离子聚合物。IssA 形成直径可达 300nm 的纳米颗粒，是已知最大的天然金属蛋白复合物。它是一个广泛分布的蛋白质家族的成员，包括固氮酶成熟因子 NifB 和 NifX。IssA 纳米颗粒在电子显微镜下可见，细胞质中呈电子致密体。纯化的纳米颗粒似乎是由含有约 6400 个铁原子和约 170 个 IssA 单体的 20nm 单元生成的。为了支持其在铁硫簇储存和簇生物合成中的作用，IssA 在体外重新组装了铁氧还蛋白中的 [4Fe-4S] 簇。
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