Department of Systems Biology, Harvard Medical School, Boston, United States.
Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, United States.
Elife. 2019 Jul 8;8:e46070. doi: 10.7554/eLife.46070.
Iron storage proteins are essential for cellular iron homeostasis and redox balance. Ferritin proteins are the major storage units for bioavailable forms of iron. Some organisms lack ferritins, and it is not known how they store iron. Encapsulins, a class of protein-based organelles, have recently been implicated in microbial iron and redox metabolism. Here, we report the structural and mechanistic characterization of a 42 nm two-component encapsulin-based iron storage compartment from . Using cryo-electron microscopy and x-ray crystallography, we reveal the assembly principles of a thermostable T = 4 shell topology and its catalytic ferroxidase cargo and show interactions underlying cargo-shell co-assembly. This compartment has an exceptionally large iron storage capacity storing over 23,000 iron atoms. Our results reveal a new approach for survival in diverse habitats with limited or fluctuating iron availability via an iron storage system able to store 10 to 20 times more iron than ferritin.
铁储存蛋白对于细胞内铁稳态和氧化还原平衡至关重要。铁蛋白是生物可利用铁形式的主要储存单元。一些生物体缺乏铁蛋白，目前尚不清楚它们如何储存铁。胶囊蛋白是一类基于蛋白质的细胞器，最近被牵连到微生物铁和氧化还原代谢中。在这里，我们报告了来自 的由 42nm 两成分胶囊蛋白组成的铁储存隔室的结构和机制特征。使用冷冻电子显微镜和 X 射线晶体学，我们揭示了热稳定的 T=4 壳拓扑结构及其催化亚铁氧化酶货物的组装原理，并显示了货物-壳共组装的基础相互作用。这个隔室具有异常大的铁储存能力，可储存超过 23000 个铁原子。我们的结果揭示了一种通过铁储存系统在有限或波动的铁供应的各种生境中生存的新方法，这种铁储存系统能够储存比铁蛋白多 10 到 20 倍的铁。
