Department of Life Sciences, Ben Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel.
J Struct Biol. 2012 Dec;180(3):479-87. doi: 10.1016/j.jsb.2012.08.001. Epub 2012 Aug 15.
Magnetotactic bacteria enclose the magnetosome, a unique prokaryotic sub-cellular organelle that allows the biomineralization of magnetic nano-crystals. Membrane-coated magnetosomes are arranged into a linear chain that permits magnetotactic bacteria to navigate geomagnetic fields. Magnetosome assembly and biomineralization are controlled by conserved magnetosome-associated proteins, including MamA, a tetra-trico-peptide repeat (TPR)-containing protein that was shown to coat the magnetosome membrane. In this study, two MamA structures from Candidatus Magnetobacterium bavaricum (Mbav) were determined via X-ray crystallography. These structures confirm that Mbav MamA folds as a sequential TPR protein and shares a high degree of structural similarity with homologous MamA proteins from Magnetospirillum species. Furthermore, the two TPR-containing domains of MamA are separated by an interphylum-conserved region containing a flexible hinge that is involved in ligand binding and recognition. Finally, substantial differences were found in the local stabilization of the MamA N-terminal domain as a result of the loss of an evolutionary conserved salt bridge.
趋磁细菌将磁小体包裹起来，磁小体是一种独特的原核细胞亚细胞器，能够使磁性纳米晶体进行生物矿化。被膜包裹的磁小体排列成一条链，使趋磁细菌能够在地球磁场中导航。磁小体的组装和生物矿化受到保守的磁小体相关蛋白的控制，包括 MamA，一种含有四三肽重复（TPR）的蛋白，它被证明可以覆盖磁小体膜。在这项研究中，通过 X 射线晶体学确定了两种来自 Candidatus Magnetobacterium bavaricum（Mbav）的 MamA 结构。这些结构证实，Mbav MamA 折叠为连续的 TPR 蛋白，并与来自 Magnetospirillum 属的同源 MamA 蛋白具有高度的结构相似性。此外，MamA 的两个 TPR 结构域之间由一个跨门结构域保守区隔开，该保守区含有一个灵活的铰链，参与配体结合和识别。最后，由于失去了一个进化保守的盐桥，MamA N 端结构域的局部稳定性发生了显著变化。
