title: Bovine immunoglobulin A (IgA)-binding activities of the surface-expressed Mig protein of Streptococcus dysgalactiae.
abstract: The Mig protein of Streptococcus dysgalactiae is a type III immunoglobulin G (IgG)-binding protein, expressing IgG- and alpha2-macroglobulin (alpha2-M)-binding receptors. This study showed that the Mig protein also displays binding activities to bovine immunoglobulin A (B-IgA). Biotin-labelled bovine serum IgA bound immobilized recombinant Mig and alpha2-M receptors derived from Mig, as well as the native Mig extracted from the surface of S. dysgalactiae strain SDG8 and the alpha(2)-M receptor released from the isogenic mig mutant strain Mig8-Mt, as determined by Western blotting and ELISA. There was no B-IgA binding activity to the immobilized IgG receptor derived from Mig or the proteins in the culture supernatant from the mig mutant strain Mig7-Mt, in which expression of Mig or Mig-related peptides on the cell surface was completely abolished. In a reciprocal experiment, biotin-labelled Mig was found to bind immobilized bovine serum IgA but not human IgA (H-IgA). The binding of Mig to bovine serum IgA was competitively inhibited by unlabelled Mig, intact and truncated alpha(2)-M receptors, and bovine serum IgA, but not by the Mig-IgG receptor, H-IgA or B-IgG. The binding of Mig and partially purified bovine secretory IgA (B-sIgA) was also characterized by Western blotting. Membrane-immobilized B-sIgA did not react with the biotin-labelled Mig, whereas soluble B-sIgA showed binding activity to the immobilized alpha2-M receptor of Mig. It is therefore concluded that the 11 kDa N-terminal region of the alpha2-M receptor of the S. dysgalactiae Mig protein specifically binds soluble and immobilized bovine serum IgA, as well as soluble B-sIgA. This is believed to be the first report of a B-IgA-binding protein in S. dysgalactiae.
authors.affiliation: Veterinary Infectious Disease Organization (VIDO), Saskatoon, Saskatchewan, Canada S7N 5E31.
authors.forename: Xin-Ming
authors.initials: XM
authors.lastname: Song
authors.affiliation: Veterinary Infectious Disease Organization (VIDO), Saskatoon, Saskatchewan, Canada S7N 5E31.
authors.forename: Jose
authors.initials: J
authors.lastname: Perez-Casal
authors.affiliation: Veterinary Infectious Disease Organization (VIDO), Saskatoon, Saskatchewan, Canada S7N 5E31.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Fontaine
authors.affiliation: Canadian Bacterial Diseases Network, Calgary, Alberta, Canada2.|Veterinary Infectious Disease Organization (VIDO), Saskatoon, Saskatchewan, Canada S7N 5E31.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Potter
mesh_terms: D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D015153:Blotting, Western; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D007070:Immunoglobulin A / Q000378:metabolism*; D009154:Mutation; D010455:Peptides; D010957:Plasmids; D011485:Protein Binding; D011956:Receptors, Cell Surface; D013291:Streptococcus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D007070:Immunoglobulin A; D010455:Peptides; D011956:Receptors, Cell Surface; D000511:alpha-Macroglobulins