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Receptor for IgA in group A streptococci: cloning of the gene and characterization of the protein expressed in Escherichia coli
Author(s) -
Lindah G.,
Åkerström B.
Publication year - 1989
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1989.tb01813.x
Subject(s) - biology , immunoglobulin d , protein a/g , polyclonal antibodies , protein g , escherichia coli , microbiology and biotechnology , streptococcus pyogenes , immunoglobulin a , binding protein , streptococcus agalactiae , antibody , protein a , myeloma protein , gene , streptococcus , immunoglobulin g , biochemistry , recombinant dna , bacteria , fusion protein , genetics , staphylococcus aureus , b cell
Summary The gene for an IgA‐binding protein from a group A streptococcal strain was cloned and expressed in Escherichia coli. The IgA‐binding protein, called protein Arp, was purified on IgA‐Sepharose, allowing complete purification in a single step. Analysis of protein Arp by Western immunoblotting demonstrated a major IgA‐binding band, with an apparent molecular weight of 42kD. The purified protein was shown to bind serum IgA and secretory IgA, as well as monoclonal IgA of both subclasses. There was no binding to IgM, IgD or IgE, but a weak binding to IgG. Inhibition experiments with whole bacteria indicated that IgA and IgG bind at separate sites. Experiments with immunoglobulin fragments showed that protein Arp binds to the Fc region of both IgA and IgG. The equilibrium constant of the reaction between protein Arp and polyclonal human IgA was determined to be 5.6 × 108 M ‐1 . Amino acid sequencing of protein Arp demonstrated a direct repeat of 7 amino acids in the NH 2 ‐terminal region, a feature previously found in several streptococcal M proteins. This suggests that protein Arp, like M proteins, may be a streptococcal virulence factor.