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Three-dimensional structure of the KdpFABC complex of Escherichia coli by electron tomography of two-dimensional crystals

机译:二维晶体的电子层析成像技术分析大肠杆菌KdpFABC复合物的三维结构

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摘要

The KdpFABC complex (Kdp) functions as a K+ pump in Escherichia coli and is a member of the family of P-type ATPases. Unlike other family members, Kdp has a unique oligomeric composition and is notable for segregating K+ transport and ATP hydrolysis onto separate subunits (KdpA and KdpB, respectively). We have produced two-dimensional crystals of the KdpFABC complex within reconstituted lipid bilayers and determined its three-dimensional structure from negatively stained samples using a combination of electron tomography and real-space averaging. The resulting map is at a resolution of 2.4 nm and reveals a dimer of Kdp molecules as the asymmetric unit; however, only the cytoplasmic domains are visible due to the lack of stain penetration within the lipid bilayer. The sizes of these cytoplasmic domains are consistent with Kdp and, using a pseudoatomic model, we have described the subunit interactions that stabilize the Kdp dimer within the larger crystallographic array. These results illustrate the utility of electron tomography in structure determination of ordered assemblies, especially when disorder is severe enough to hamper conventional crystallographic analysis.
机译:KdpFABC复合物(Kdp)在大肠杆菌中起K + 泵的作用,并且是P型ATP酶家族的成员。与其他家族成员不同,Kdp具有独特的寡聚组成,并且可以将K + 转运和ATP水解分离到单独的亚基上(分别为KdpA和KdpB)。我们已经在重构的脂质双层中产生了KdpFABC复合物的二维晶体,​​并使用电子断层扫描和实空间平均相结合从负染样品中确定了其三维结构。所得图的分辨率为2.4 nm,显示出Kdp分子的二聚体为不对称单元;然而,由于缺乏脂质双层内的染色渗透,仅可见胞质结构域。这些胞质域的大小与Kdp一致,并且使用伪原子模型,我们描述了在较大的晶体学阵列内稳定Kdp二聚体的亚基相互作用。这些结果说明了电子断层扫描在确定有序组件的结构中的实用性,尤其是当混乱严重到足以妨碍常规晶体学分析时。

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