The acidic repetitive domain of the Magnetospirillum gryphiswaldense MamJ protein displays hypervariability but is not required for magnetosome chain assembly
The acidic repetitive domain of the Magnetospirillum gryphiswaldense MamJ protein displays hypervariability but is not required for magnetosome chain assembly
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DOI：
10.1128/jb.00421-07
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发表时间：
2007-09-01
影响因子：
3.2
通讯作者：
Schueler, Dirk
中科院分区：
文献类型：
--
作者：
Scheffel, Andre;Schueler, Dirk
趋磁细菌利用磁小体链沿着地球磁场导航，磁小体是由膜封闭的磁铁矿晶体组成的细胞内细胞器。高度有序的磁小体链的组装受遗传控制，涉及几种特定的蛋白质。基于遗传学和冷冻电子断层扫描研究，最近提出了一种模型，其中酸性MamJ磁小体蛋白将磁小体囊泡附着到由MamK形成的肌动蛋白样细胞骨架丝上，从而防止磁小体链崩溃。然而，确切的功能以及MamK和MamJ之间的相互作用模式是未知的。在这里，我们证明了几个功能性的MamJ变体从Magnetocellum gryphiswaldense和其他趋磁细菌共享一个酸性的和重复的中央域，它显示了一个不寻常的种内和种间序列多态性，可能是由相同的拷贝之间的同源重组的Glu和Pro丰富的重复。令人惊讶的是，mamj突变等位基因，其中中央结构域被删除保留其潜力，恢复链形成在一个三角洲manJ突变，这表明酸性结构域是不是必不可少的MamJ的功能。双杂交实验的结果表明，MamJ与MamK发生物理相互作用，并且MamJ内的两个不同序列区域参与与MamK的结合。缺乏任一结合结构域的MamJ的突变变体不能在功能上补充Delta mamJ突变体。此外，双杂交实验表明MamJ的两个MamK结合结构域赋予MamJ的寡聚化。总之，我们的数据揭示了MamJ蛋白在链组装和维护中的功能所需的结构域，并提供了MamJ和细胞骨架丝蛋白MamK之间直接相互作用的第一个实验指标。
Magnetotactic bacteria navigate along the earth's magnetic field using chains of magnetosomes, which are intracellular organelles comprising membrane-enclosed magnetite crystals. The assembly of highly ordered magnetosome chains is under genetic control and involves several specific proteins. Based on genetic and cryo-electron tomography studies, a model was recently proposed in which the acidic MamJ magnetosome protein attaches magnetosome vesicles to the actin-like cytoskeletal filament formed by MamK, thereby preventing magnetosome chains from collapsing. However, the exact functions as well as the mode of inter,action between MamK and MamJ are unknown. Here, we demonstrate that several functional MamJ variants from Magnetospirillum gryphiswaldense and other magnetotactic bacteria share an acidic and repetitive central domain, which displays an unusual intra- and interspecies sequence polymorphism, probably caused by homologous recombination between identical copies of Glu- and Pro-rich repeats. Surprisingly, mamj mutant alleles in which the central domain was deleted retained their potential to restore chain formation in a Delta manJ mutant, suggesting that the acidic domain is not essential for MamJ's function. Results of two-hybrid experiments indicate that MamJ physically interacts with MamK, and two distinct sequence regions within MamJ were shown to be involved in binding to MamK. Mutant variants of MamJ lacking either of the binding domains were unable to functionally complement the Delta mamJ mutant. In addition, two-hybrid experiments suggest both MamK-binding domains of MamJ confer oligomerization of MamJ. In summary, our data reveal domains required for the functions of the MamJ protein in chain assembly and maintenance and provide the first experimental indications for a direct interaction between MamJ and the cytoskeletal filament protein MamK.