Anthrax Toxin Receptor Drives Protective Antigen Oligomerization and Stabilizes the Heptameric and Octameric Oligomer by a Similar Mechanism
Anthrax Toxin Receptor Drives Protective Antigen Oligomerization and Stabilizes the Heptameric and Octameric Oligomer by a Similar Mechanism
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DOI：
10.1371/journal.pone.0013888
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发表时间：
2010-11-08
期刊：
影响因子：
3.7
通讯作者：
Krantz, Bryan A.
中科院分区：
文献类型：
--
作者：
Kintzer, Alexander F.;Sterling, Harry J.;Krantz, Bryan A.
研究背景：炭疽毒素由保护性抗原（PA）、致死因子（LF）和水肿因子（EF）组成。这些蛋白质是单独无毒的;然而，当PA与LF和EF组装时，它分别产生致死毒素和水肿毒素。组装发生在细胞表面或血浆中。在每个环境中，PA组装成结合LF和EF的七聚体和八聚体复合物的混合物。虽然八聚体PA是在生理条件（pH 7.4，37 ° C）下在血浆中鉴定的主要形式，但七聚体PA在细胞表面上更普遍。这两种环境之间的区别在于炭疽毒素受体（ANTXR）与细胞表面的PA结合。已知细胞外ANTXR结构域通过防止过早的PA通道形成（一种使毒素失活的过程）来稳定含有PA七聚体的毒素复合物。ANTXR在PA寡聚化和在稳定的毒素复合物中含有八聚体PA的作用是不理解的。方法：使用荧光组装测定，我们表明，细胞外ANTXR结构域驱动PA寡聚化。此外，相对于单体ANTXR构建体，二聚体ANTXR构建体增加PA组装的程度并加速PA组装的速率。质谱分析表明，七聚体和八聚体PA低聚物结合ANTXR结构域的完全化学计量互补。电子显微镜和圆二色性研究表明，这两个不同的PA低聚物同样稳定的ANTXR interactions.Conclusions：我们建议，PA寡聚化是由二聚体ANTXR复合物细胞表面。通过它们与ANTXR的相互作用，含有七聚体和八聚体PA寡聚体的毒素复合物被类似地稳定化。考虑到PA七聚体和细胞外组装途径在血浆中确定的相对不稳定性，我们提出了一种方法来调节炭疽发病过程中感染部位周围毒素梯度的发展。
Background: Anthrax toxin is comprised of protective antigen (PA), lethal factor (LF), and edema factor (EF). These proteins are individually nontoxic; however, when PA assembles with LF and EF, it produces lethal toxin and edema toxin, respectively. Assembly occurs either on cell surfaces or in plasma. In each milieu, PA assembles into a mixture of heptameric and octameric complexes that bind LF and EF. While octameric PA is the predominant form identified in plasma under physiological conditions (pH 7.4, 37 degrees C), heptameric PA is more prevalent on cell surfaces. The difference between these two environments is that the anthrax toxin receptor (ANTXR) binds to PA on cell surfaces. It is known that the extracellular ANTXR domain serves to stabilize toxin complexes containing the PA heptamer by preventing premature PA channel formation-a process that inactivates the toxin. The role of ANTXR in PA oligomerization and in the stabilization of toxin complexes containing octameric PA are not understood.Methodology: Using a fluorescence assembly assay, we show that the extracellular ANTXR domain drives PA oligomerization. Moreover, a dimeric ANTXR construct increases the extent of and accelerates the rate of PA assembly relative to a monomeric ANTXR construct. Mass spectrometry analysis shows that heptameric and octameric PA oligomers bind a full stoichiometric complement of ANTXR domains. Electron microscopy and circular dichroism studies reveal that the two different PA oligomers are equally stabilized by ANTXR interactions.Conclusions: We propose that PA oligomerization is driven by dimeric ANTXR complexes on cell surfaces. Through their interaction with the ANTXR, toxin complexes containing heptameric and octameric PA oligomers are similarly stabilized. Considering both the relative instability of the PA heptamer and extracellular assembly pathway identified in plasma, we propose a means to regulate the development of toxin gradients around sites of infection during anthrax pathogenesis.