title: Monitoring anthrax toxin receptor dissociation from the protective antigen by NMR.
abstract: The binding of the Bacillus anthracis protective antigen (PA) to the host cell receptor is the first step toward the formation of the anthrax toxin, a tripartite set of proteins that include the enzymatic moieties edema factor (EF), and lethal factor (LF). PA is cleaved by a furin-like protease on the cell surface followed by the formation of a donut-shaped heptameric prepore. The prepore undergoes a major structural transition at acidic pH that results in the formation of a membrane spanning pore, an event which is dictated by interactions with the receptor and necessary for entry of EF and LF into the cell. We provide direct evidence using 1-dimensional (13)C-edited (1)H NMR that low pH induces dissociation of the Von-Willebrand factor A domain of the receptor capillary morphogenesis protein 2 (CMG2) from the prepore, but not the monomeric full length PA. Receptor dissociation is also observed using a carbon-13 labeled, 2-fluorohistidine labeled CMG2, consistent with studies showing that protonation of His-121 in CMG2 is not a mechanism for receptor release. Dissociation is likely caused by the structural transition upon formation of a pore from the prepore state rather than protonation of residues at the receptor PA or prepore interface.
authors.affiliation: Department of Chemistry, Wichita State University, Wichita, Kansas 67226, USA.
authors.forename: Maheshinie
authors.initials: M
authors.lastname: Rajapaksha
authors.forename: Jack F
authors.initials: JF
authors.lastname: Eichler
authors.forename: Jan
authors.initials: J
authors.lastname: Hajduch
authors.forename: David E
authors.initials: DE
authors.lastname: Anderson
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Kirk
authors.forename: James G
authors.initials: JG
authors.lastname: Bann
mesh_terms: D000942:Antigens, Bacterial / Q000737:chemistry / Q000378:metabolism*; D001408:Bacillus anthracis / Q000378:metabolism*; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism*; D002247:Carbon Isotopes / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding / Q000502:physiology; D018000:Receptors, Peptide; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: C447150:ANTXR2 protein, human; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D002247:Carbon Isotopes; D008565:Membrane Proteins; D018000:Receptors, Peptide; C030325:anthrax toxin; D014841:von Willebrand Factor; D006639:Histidine