title: Divalent metal ion coordination by residue T118 of anthrax toxin receptor 2 is not essential for protective antigen binding.
abstract: The protective antigen (PA) subunit of anthrax toxin interacts with the integrin-like I domains of either of two cellular receptors, ANTXR1 or ANTXR2. These I domains contain a metal ion-dependent adhesion site (MIDAS) made up of five non-consecutive amino acid residues that coordinate a divalent metal ion that is important for PA-binding. The MIDAS residues of integrin I domains shift depending upon whether the domain exists in a closed (ligand-unbound) or open (ligand-bound) conformation. Of relevance to this study, the MIDAS threonine residue coordinates the metal ion only in the open I domain conformation. Previously it was shown that the MIDAS threonine is essential for PA interaction with ANTXR1, a result consistent with the requirement that the I domain of that receptor adopts an open conformation for PA-binding. Here we have tested the requirement for the MIDAS threonine of ANTXR2 for PA-binding. We show that the toxin can bind to a mutant receptor lacking the MIDAS threonine and that it can use that mutant receptor to intoxicate cultured cells. These findings suggest that an open-like configuration of the ANTXR2 MIDAS is not essential for the interaction with PA.
authors.affiliation: Infectious Disease Laboratory, Salk Institute for Biological Studies, La Jolla, California, United States of America.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Scobie
authors.forename: John A T
authors.initials: JA
authors.lastname: Young
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000737:chemistry / Q000378:metabolism*; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D016466:CHO Cells; D002413:Cations, Divalent / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D018000:Receptors, Peptide; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013912:Threonine / Q000737:chemistry
chemical_list: C447150:ANTXR2 protein, human; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D002413:Cations, Divalent; D008565:Membrane Proteins; D018000:Receptors, Peptide; D011993:Recombinant Fusion Proteins; C030325:anthrax toxin; D013912:Threonine