The Tp0684 (MglB-2) Lipoprotein of Treponema pallidum: A Glucose-Binding Protein with Divergent Topology.
The Tp0684 (MglB-2) Lipoprotein of Treponema pallidum: A Glucose-Binding Protein with Divergent Topology.
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DOI：
10.1371/journal.pone.0161022
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发表时间：
2016
期刊：
影响因子：
3.7
通讯作者：
Norgard MV
中科院分区：
文献类型：
--
作者：
Brautigam CA;Deka RK;Liu WZ;Norgard MV
梅毒螺旋体是引起梅毒的细菌，是一种专性的人类寄生虫。因此，它必须从宿主那里以碳源的形式获取能量。有充分的证据表明，这种螺旋体的主要能量来源是通过ABC转运体从其环境中获得的d -葡萄糖。此外，有遗传证据表明，T. pallidum中存在d -葡萄糖趋化系统。这两个过程都可能依赖于一个单一的脂化化学受体：Tp0684，也被称为TpMglB-2，因为它的序列与大肠杆菌的MglB同源。为了扩大我们对这种潜在的重要蛋白质的理解，我们确定了重组蛋白可溶性形式的2.05-Å x射线晶体结构。与TpMglB-2一样，TpMglB-2采用与其他ABC转运蛋白的配体结合蛋白（lbp）相似的双叶折叠。然而，这种蛋白质具有不寻常的圆形排列拓扑结构。这一特征促使了一系列的生物物理研究，以检验蛋白质的拓扑特征是否影响其假定的化学受体功能。差示扫描荧光法和等温滴定量热法证实，蛋白质结合d -葡萄糖在其两个裂片之间的间隙。此外，利用超离心分析揭示了d -葡萄糖结合伴随着显著的构象变化。因此，TpMglB-2在体外似乎具有完全的功能，并且考虑到该蛋白对苍白球绦虫生理学的可能核心重要性，我们的研究结果对这种专性人类病原体的生存能力和致病性具有重要意义。
Treponema pallidum, the bacterium that causes syphilis, is an obligate human parasite. As such, it must acquire energy, in the form of carbon sources, from the host. There is ample evidence that the principal source of energy for this spirochete is D-glucose acquired from its environment, likely via an ABC transporter. Further, there is genetic evidence of a D-glucose chemotaxis system in T. pallidum. Both of these processes may be dependent on a single lipidated chemoreceptor: Tp0684, also called TpMglB-2 for its sequence homology to MglB of Escherichia coli. To broaden our understanding of this potentially vital protein, we determined a 2.05-Å X-ray crystal structure of a soluble form of the recombinant protein. Like its namesake, TpMglB-2 adopts a bilobed fold that is similar to that of the ligand-binding proteins (LBPs) of other ABC transporters. However, the protein has an unusual, circularly permuted topology. This feature prompted a series of biophysical studies that examined whether the protein’s topological distinctiveness affected its putative chemoreceptor functions. Differential scanning fluorimetry and isothermal titration calorimetry were used to confirm that the protein bound D-glucose in a cleft between its two lobes. Additionally, analytical ultracentrifugation was employed to reveal that D-glucose binding is accompanied by a significant conformational change. TpMglB-2 thus appears to be fully functional in vitro, and given the probable central importance of the protein to T. pallidum’s physiology, our results have implications for the viability and pathogenicity of this obligate human pathogen.