title: Anthrax Toxin Protective Antigen Variants That Selectively Utilize either the CMG2 or TEM8 Receptors for Cellular Uptake and Tumor Targeting.
abstract: The protective antigen (PA) moiety of anthrax toxin binds to cellular receptors and mediates the translocation of the two enzymatic moieties of the toxin to the cytosol. Two PA receptors are known, with capillary morphogenesis protein 2 (CMG2) being the more important for pathogenesis and tumor endothelial marker 8 (TEM8) playing a minor role. The C-terminal PA domain 4 (PAD4) has extensive interactions with the receptors and is required for binding. Our previous study identified PAD4 variants having enhanced TEM8 binding specificity. To obtain PA variants that selectively bind to CMG2, here we performed phage display selections using magnetic beads having bound CMG2. We found that PA residue isoleucine 656 plays a critical role in PA binding to TEM8 but has a much lesser effect on PA binding to CMG2. We further characterized the role of residue 656 in distinguishing PA binding to CMG2 versus TEM8 by substituting it with the other 19 amino acids. Of the resulting variants, PA I656Q and PA I656V had significantly reduced activity on TEM8-expressing CHO cells but maintained their activity on CMG2-expressing CHO cells. The preference of these PA mutants for CMG2 over TEM8 was further demonstrated using mouse embryonic fibroblast cells and mice deficient in the CMG2 and/or the TEM8 receptors. The structural basis of the alterations in the receptor binding activities of these mutants is also discussed.
authors.affiliation: From the Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892-3202 and.
authors.forename: Kuang-Hua
authors.initials: KH
authors.lastname: Chen
authors.affiliation: From the Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892-3202 and the Proteases and Tissue Remodeling Section, Oral and Pharyngeal Cancer Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Shihui
authors.initials: S
authors.lastname: Liu
authors.affiliation: From the Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892-3202 and.
authors.forename: Clinton E
authors.initials: CE
authors.lastname: Leysath
authors.affiliation: From the Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892-3202 and.
authors.forename: Sharmina
authors.initials: S
authors.lastname: Miller-Randolph
authors.affiliation: From the Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892-3202 and.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: From the Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892-3202 and.
authors.forename: Rasem
authors.initials: R
authors.lastname: Fattah
authors.affiliation: the Proteases and Tissue Remodeling Section, Oral and Pharyngeal Cancer Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Bugge
authors.affiliation: From the Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892-3202 and sleppla@niaid.nih.gov.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Leppla
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism*; D001408:Bacillus anthracis / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004622:Embryo, Mammalian; D005347:Fibroblasts; D051379:Mice; D008840:Microfilament Proteins; D020125:Mutation, Missense; D011485:Protein Binding; D000072417:Protein Domains; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D000942:Antigens, Bacterial; C523012:Antxr1 protein, mouse; C523013:Antxr2 protein, mouse; D001427:Bacterial Toxins; D014408:Biomarkers, Tumor; D008840:Microfilament Proteins; D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C030325:anthrax toxin
keywords: CMG2; TEM8; anthrax toxin; mutagenesis in vitro; phage display; protective antigen; receptor; tumor therapy