MamO Is a Repurposed Serine Protease that Promotes Magnetite Biomineralization through Direct Transition Metal Binding in Magnetotactic Bacteria.
MamO Is a Repurposed Serine Protease that Promotes Magnetite Biomineralization through Direct Transition Metal Binding in Magnetotactic Bacteria.
复制标题
MAMO是一种重新利用的丝氨酸蛋白酶，可通过磁性细菌中直接过渡金属结合促进磁铁矿生物矿化。
DOI：
10.1371/journal.pbio.1002402
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发表时间：
2016-03
期刊：
影响因子：
9.8
通讯作者：
Komeili A
中科院分区：
文献类型：
--
作者：
Hershey DM;Ren X;Melnyk RA;Browne PJ;Ozyamak E;Jones SR;Chang MC;Hurley JH;Komeili A
许多生物体将无机原子转化为高度有序的晶体材料。这种生物矿化过程的一个典型例子是在趋磁细菌中产生纳米级磁性晶体。先前的研究表明，两种假定的丝氨酸蛋白酶 MamE 和 MamO 参与了磁性螺菌 AMB-1 中磁铁矿形成的早期阶段。在这里，通过遗传分析和 X 射线晶体学，我们发现 MamO 具有简并的活性位点，使其无法发挥蛋白酶活性。相反，MamO 通过两种遗传上不同的非催化活性促进磁小体形成：激活 MamE 依赖性生物矿化因子的蛋白水解作用以及与过渡金属离子的直接结合。通过解析与金属离子结合的蛋白酶结构域的结构，我们鉴定了 MamO 中表面暴露的二组氨酸基序，该基序有助于金属结合，并表明它是启动体内生物矿化所必需的。最后，我们发现假蛋白酶在趋磁细菌中广泛存在，并且它们在三个不同的分类群中独立进化。我们的结果强调了蛋白质支架在适应新的生化活动方面的多功能性，并为生物矿化的最早阶段提供了前所未有的见解。遗传、结构和系统发育分析表明，MamO 是丝氨酸蛋白酶的简并后代，在促进细菌中磁性氧化铁颗粒的合成方面获得了新功能。生物矿化是一个古老而普遍的过程，生物体通过该过程为了自身利益而组装晶体材料。将无机原子精确组织成形状复杂的晶体的能力证明了对纳米粒子合成的一定程度的控制，这让几代生物学家着迷。我们一直在研究一组称为趋磁细菌的微生物如何合成用于沿磁场导航的铁基晶体。在这里，我们描述了一种名为 MamO 的蛋白质，它有助于在趋磁细菌 MagentospirillumMagneticum AMB-1 的细胞中启动一种称为磁铁矿的磁性矿物的形成。尽管预计是一种胰蛋白酶样蛋白酶，但我们发现 MamO 已经失去了其祖先的催化活性，而是获得了作为金属结合支架的新功能。通过解析其结构，我们发现了 MamO 如何与过渡金属原子结合，并表明这种活性是细胞内磁铁矿结晶所必需的。令人惊讶的是，我们发现类似的重新利用的胰蛋白酶样蛋白酶在所有三个主要趋磁组中都独立进化，概述了一个令人着迷的趋同进化案例。 MamO 独特的进化历史表明，现有的蛋白质支架可以被修改以提供新的功能，并有助于我们了解细胞如何构建基于过渡金属的矿物质。
Many living organisms transform inorganic atoms into highly ordered crystalline materials. An elegant example of such biomineralization processes is the production of nano-scale magnetic crystals in magnetotactic bacteria. Previous studies implicated the involvement of two putative serine proteases, MamE and MamO, during the early stages of magnetite formation in Magnetospirillum magneticum AMB-1. Here, using genetic analysis and X-ray crystallography, we show that MamO has a degenerate active site, rendering it incapable of protease activity. Instead, MamO promotes magnetosome formation through two genetically distinct, noncatalytic activities: activation of MamE-dependent proteolysis of biomineralization factors and direct binding to transition metal ions. By solving the structure of the protease domain bound to a metal ion, we identify a surface-exposed di-histidine motif in MamO that contributes to metal binding and show that it is required to initiate biomineralization in vivo. Finally, we find that pseudoproteases are widespread in magnetotactic bacteria and that they have evolved independently in three separate taxa. Our results highlight the versatility of protein scaffolds in accommodating new biochemical activities and provide unprecedented insight into the earliest stages of biomineralization. Genetic, structural, and phylogenetic analyses reveal that MamO is a degenerate descendant of serine proteases that has acquired a new function in promoting the synthesis of magnetic iron oxide particles in bacteria. Biomineralization is an ancient and ubiquitous process by which organisms assemble crystalline materials for their own benefit. The ability to precisely organize inorganic atoms into crystals with intricate shapes demonstrates a level of control over nanoparticle synthesis that has fascinated biologists for generations. We have been studying how a group of microorganisms, called magnetotactic bacteria, synthesizes iron-based crystals that are used for navigation along magnetic fields. Here, we characterize a protein called MamO that helps to initiate the formation of a magnetic mineral called magnetite in cells of the magnetotactic bacterium Magentospirillum magneticum AMB-1. Although predicted to be a trypsin-like protease, we show that MamO has lost its ancestral catalytic activity and instead gained a new function as a metal-binding scaffold. By solving its structure, we discovered how MamO binds to transition metal atoms and show that this activity is required to crystalize magnetite within cells. Surprisingly, we find that similar repurposed trypsin-like proteases have evolved independently in all three major magnetotactic groups, outlining a fascinating case of convergent evolution. The unique evolutionary history of MamO demonstrates that existing protein scaffolds can be modified to provide new functions and contributes to our understanding of how cells build transition metal-based minerals.