Structural characterisation of the virulence-associated protein VapG from the horse pathogen Rhodococcus equi.
Structural characterisation of the virulence-associated protein VapG from the horse pathogen Rhodococcus equi.
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DOI：
10.1016/j.vetmic.2015.01.027
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发表时间：
2015-08-31
影响因子：
3.3
通讯作者：
Wilkinson AJ
中科院分区：
文献类型：
--
作者：
Okoko T;Blagova EV;Whittingham JL;Dover LG;Wilkinson AJ
确定了马红球菌毒力蛋白的 3 维结构。 VapG 包含一个闭合 β 桶结构域，其前面是一个天然无序区域。 VapB、VapD和VapG的结构紧密重叠。 VAP 结构缺乏可识别的配体或蛋白质结合位点。吞噬体诱导的构象变化可能是毒力所必需的。马红球菌的毒力和宿主范围取决于其毒力质粒的可变致病性岛。值得注意的基因产物是一个对巨噬细胞内增殖至关重要的小分泌毒力相关蛋白 (Vap) 家族。马适应菌株会在马驹中引起严重的化脓性肉芽肿性肺炎，产生毒力所必需的细胞相关的 VapA 以及其他五种分泌的同源物。在缺乏生化洞察力的情况下，人们的注意力转向这些蛋白质的结构以发展功能假设。最近的研究描述了 VapD 和猪适应菌株 VapA 直系同源物的截短物 VapB 的晶体结构。在这里，我们结晶了全长 VapG 并通过分子置换确定了其结构。对应于 N 末端结构域的电子密度不可见，表明它是无序的。蛋白质核心采用紧凑的椭圆形、反平行 β 桶折叠，具有 β1-β2-β3-β8-β5-β6-β7-β4 拓扑结构，并由该家族独有的单个外围 α 螺旋装饰。蛋白质的高甘氨酸含量允许二级结构元件紧密堆积。从拓扑上讲，表面没有表明分子相互作用的联系的凹痕。 VapG表面极性基团和非极性基团的分布明显不均匀。三分之一的表面主要是暴露的非极性侧链，没有可电离的侧链，只有四个极性侧链暴露，形成了广阔的平坦疏水表面。其他表面区域极性更强，特别是在 α 螺旋上或附近以及围绕 β 桶中心的带。讨论了这些最新结构可能的功能意义。
The 3-dimensional structure of a Rhodococcus equi virulence protein was determined. VapG comprises a closed beta barrel domain preceded by a natively disordered region. The structures of VapB, VapD and VapG are closely superimposable. The VAP structures lack recognisable ligand or protein binding sites. Phagosome-induced conformational changes may be required for virulence. Virulence and host range in Rhodococcus equi depends on the variable pathogenicity island of their virulence plasmids. Notable gene products are a family of small secreted virulence-associated proteins (Vaps) that are critical to intramacrophagic proliferation. Equine-adapted strains, which cause severe pyogranulomatous pneumonia in foals, produce a cell-associated VapA that is necessary for virulence, alongside five other secreted homologues. In the absence of biochemical insight, attention has turned to the structures of these proteins to develop a functional hypothesis. Recent studies have described crystal structures for VapD and a truncate of the VapA orthologue of porcine-adapted strains, VapB. Here, we crystallised the full-length VapG and determined its structure by molecular replacement. Electron density corresponding to the N-terminal domain was not visible suggesting that it is disordered. The protein core adopted a compact elliptical, anti-parallel β-barrel fold with β1–β2–β3–β8–β5–β6–β7–β4 topology decorated by a single peripheral α-helix unique to this family. The high glycine content of the protein allows close packing of secondary structural elements. Topologically, the surface has no indentations that indicate a nexus for molecular interactions. The distribution of polar and apolar groups on the surface of VapG is markedly uneven. One-third of the surface is dominated by exposed apolar side-chains, with no ionisable and only four polar side-chains exposed, giving rise to an expansive flat hydrophobic surface. Other surface regions are more polar, especially on or near the α-helix and a belt around the centre of the β-barrel. Possible functional significance of these recent structures is discussed.