1] Commissariat à l'Energie Atomique et aux Energies Alternatives, Direction des Sciences du Vivant, Institut de Biologie Environnementale et de Biotechnologies,, F-13108, France [2] Centre National de la Recherche Scientifique, Unité Mixte de Recherche Biologie Végétale et Microbiologie Environnementales, Saint-Paul-lez-Durance, F-13108, France [3] Aix-Marseille Université, Saint-Paul-lez-Durance, F-13108, France.
Nature. 2013 Oct 31;502(7473):681-4. doi: 10.1038/nature12573. Epub 2013 Oct 6.
Magnetotactic bacteria align along the Earth's magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe(II)Fe(III)2O4) or greigite (Fe(II)Fe(III)2S4) crystal embedded in a lipid vesicle. Although the need for both iron(II) and iron(III) is clear, little is known about the biological mechanisms controlling their ratio. Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron(II) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron(III) ferrihydrite eventually required for magnetite crystal growth in vivo. These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization.
趋磁细菌利用一种称为磁小体的细胞器沿着地球磁场排列，磁小体是一种嵌入在脂质泡中的生物矿化磁铁矿（Fe(II)Fe(III)2O4）或陨硫铁（Fe(II)Fe(III)2S4）晶体。尽管清楚地需要铁(II)和铁(III)，但对于控制它们比例的生物学机制知之甚少。在这里，我们展示了磁小体相关蛋白 MamP 的结构，并发现它建立在一个独特的自插 PDZ 结构域与两个磁敏蛋白结构域融合的基础上，定义了一类新的 c 型细胞色素，仅存在于趋磁细菌中。突变分析、酶动力学、与铁(II)共结晶以及体外 MamP 辅助磁铁矿生产测定表明，MamP 是一种铁氧化酶，有助于形成铁(III)水铁矿，最终为体内磁铁矿晶体生长所必需。这些结果证明了磁小体内发生的铁管理的分子机制，并强调了磁敏蛋白在铁生物矿化中的作用。
