作者: Belle, Archana ; Haase, Simone ; Pawlik, Jennifer ; Trilling, Anke K. ; Geren, Isin N. ; Deppe, Dorothée ; Wycoff, Keith L. ; Schaefer, Leah ; Maclean, James M. ; Leppla, Stephen H. ; Peterson, Johnny W. ; Liu, Shihui

ABSTRACT Inhalational anthrax, a zoonotic disease caused by the inhalation of Bacillus anthracis spores, has a ∼50% fatality rate even when treated with antibiotics. Pathogenesis is dependent on the activity of two toxic noncovalent complexes: edema toxin (EdTx) and lethal toxin (LeTx). Protective antigen (PA), an essential component of both complexes, binds with high affinity to the major receptor mediating the lethality of anthrax toxin in vivo , capillary morphogenesis protein 2 (CMG2). Certain antibodies against PA have been shown to protect against anthrax in vivo . As an alternative to anti-PA antibodies, we produced a fusion of the extracellular domain of human CMG2 and human IgG Fc, using both transient and stable tobacco plant expression systems. Optimized expression led to the CMG2-Fc fusion protein being produced at high levels: 730 mg/kg fresh leaf weight in Nicotiana benthamiana and 65 mg/kg in N. tabacum . CMG2-Fc, purified from tobacco plants, fully protected rabbits against a lethal challenge with B. anthracis spores at a dose of 2 mg/kg body weight administered at the time of challenge. Treatment with CMG2-Fc did not interfere with the development of the animals' own immunity to anthrax, as treated animals that survived an initial challenge also survived a rechallenge 30 days later. The glycosylation of the Fc (or lack thereof) had no significant effect on the protective potency of CMG2-Fc in rabbits or on its serum half-life, which was about 5 days. Significantly, CMG2-Fc effectively neutralized, in vitro , LeTx-containing mutant forms of PA that were not neutralized by anti-PA monoclonal antibodies.

Toxins2区 · 医学

Recombinant HSA-CMG2 Is a Promising Anthrax Toxin Inhibitor

2区 · 医学

ArticleOA

作者: Yin, Ying ; Xu, Junjie ; Dong, Dayong ; Fu, Ling ; Li, Liangliang ; Guo, Qiang ; Liu, Ju ; Chen, Wei ; Zhang, Jun

Anthrax toxin is the major virulence factor produced by Bacillus anthracis. Protective antigen (PA) is the key component of the toxin and has been confirmed as the main target for the development of toxin inhibitors. The inhibition of the binding of PA to its receptor, capillary morphogenesis protein-2 (CMG2), can effectively block anthrax intoxication. The recombinant, soluble von Willebrand factor type A (vWA) domain of CMG2 (sCMG2) has demonstrated potency against anthrax toxin. However, the short half-life of sCMG2 in vivo is a disadvantage for its development as a new anthrax drug. In the present study, we report that HSA-CMG2, a protein combining human serum albumin (HSA) and sCMG2, produced in the Pichia pastoris expression system prolonged the half-life of sCMG2 while maintaining PA binding ability. The IC50 of HSA-CMG2 is similar to those of sCMG2 and CMG2-Fc in in vitro toxin neutralization assays, and HSA-CMG2 completely protects rats from lethal doses of anthrax toxin challenge; these same challenge doses exceed sCMG2 at a sub-equivalent dose ratio and overwhelm CMG2-Fc. Our results suggest that HSA-CMG2 is a promising inhibitor of anthrax toxin and may contribute to the development of novel anthrax drugs.

PLoS ONE3区 · 综合性期刊

Improving the Anti-Toxin Abilities of the CMG2-Fc Fusion Protein with the Aid of Computational Design

3区 · 综合性期刊

ArticleOA

作者: Xi, Yongyi ; Hu, Xianwen ; Yue, Junjie ; Chen, Huipeng ; Gao, Lihua ; Peng, Hui ; Chen, Hongxing ; Shao, Yong ; Wu, Xiaojie

CMG2-Fc is a fusion protein composed of the extracellular domain of capillary morphogenesis protein 2 (CMG2) and the Fc region of human immunoglobulin G; CMG2-Fc neutralizes anthrax toxin and offers protection against Bacillus anthracis challenge. To enhance the efficacy of CMG2-Fc against anthrax toxin, we attempted to engineer a CMG2-Fc with an improved affinity for PA. Using the automatic design algorithm FoldX and visual inspection, we devised two CMG2-Fc variants that introduce mutations in the CMG2 binding interface and improve the computationally assessed binding affinity for PA. An experimental affinity assay revealed that the two variants showed increased binding affinity, and in vitro and in vivo toxin neutralization testing indicated that one of these mutants (CMG2-Fc(E117Q)) has superior activity against anthrax toxin and was suitable for further development as a therapeutic agent for anthrax infections. This study shows that the computational design of the PA binding interface of CMG2 to obtain CMG2-Fc variants with improving anti-toxin abilities is viable. Our results demonstrate that computational design can be further applied to generate other CMG2-Fc mutants with greatly improved therapeutic efficacy.

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