Scobie Heather M, Rainey G Jonah A, Bradley Kenneth A, Young John A T
McArdle Laboratory for Cancer Research, University of Wisconsin, Madison, WI 53706, USA.
Proc Natl Acad Sci U S A. 2003 Apr 29;100(9):5170-4. doi: 10.1073/pnas.0431098100. Epub 2003 Apr 16.
Bacillus anthracis secretes two bipartite toxins thought to be involved in anthrax pathogenesis and resulting death of the host. The current model for intoxication is that protective antigen (PA) toxin subunits bind a single group of cell-surface anthrax toxin receptors (ATRs), encoded by the tumor endothelial marker 8 (TEM8) gene. The ATR/TEM8-PA interaction is mediated by the receptor's extracellular domain related to von Willebrand factor type A or integrin inserted domains (VWA/I domains). A metal ion-dependent adhesion site (MIDAS) located within this domain of the ATR/TEM8 protein chelates a divalent cation critical for PA binding. In this report, we identify a second PA receptor encoded by capillary morphogenesis gene 2 (CMG2), which has 60% amino acid identity to ATR/TEM8 within the VWA/I domain, as well as a conserved MIDAS motif. A recombinant CMG2 protein bound PA and mediated toxin internalization when expressed on receptor-deficient cells. Binding between the CMG2 VWA/I domain and PA was shown to be direct and metal-dependent, although the cation specificity of this interaction is different than that observed with ATR/TEM8. Northern blot analysis revealed that CMG2 is widely expressed in human tissues, indicating that this receptor is likely to be relevant for disease pathogenesis. Finally, a soluble version of the CMG2 VWA/I domain inhibited intoxication of cells expressing endogenous toxin receptors when it was added to PA at a 3:1 ratio. These studies distinguish CMG2 as a second anthrax toxin receptor and identify a potent antitoxin that may prove useful for the treatment of anthrax.
炭疽芽孢杆菌分泌两种二分体毒素，据认为这两种毒素与炭疽病发病机制及宿主死亡有关。目前的中毒模型是，保护性抗原（PA）毒素亚基结合由肿瘤内皮标志物8（TEM8）基因编码的一组细胞表面炭疽毒素受体（ATR）。ATR/TEM8-PA相互作用由与A型血管性血友病因子或整合素插入结构域（VWA/I结构域）相关的受体细胞外结构域介导。位于ATR/TEM8蛋白该结构域内的金属离子依赖性粘附位点（MIDAS）螯合对PA结合至关重要的二价阳离子。在本报告中，我们鉴定出由毛细血管形态发生基因2（CMG2）编码的第二种PA受体，它在VWA/I结构域内与ATR/TEM8具有60%的氨基酸同一性，并且还有一个保守的MIDAS基序。当在缺乏受体的细胞上表达时，重组CMG2蛋白结合PA并介导毒素内化。CMG2的VWA/I结构域与PA之间的结合显示是直接的且依赖金属，尽管这种相互作用的阳离子特异性与ATR/TEM8所观察到的不同。Northern印迹分析显示CMG2在人体组织中广泛表达，表明该受体可能与疾病发病机制相关。最后，当以3:1的比例添加到PA中时，CMG2的VWA/I结构域的可溶性形式抑制表达内毒素受体的细胞中毒。这些研究将CMG2区分为第二种炭疽毒素受体，并鉴定出一种可能对炭疽治疗有用的强效抗毒素。
