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  • Title: Identification of the IgA-binding region in streptococcal protein Arp.
    Author: Johnsson E, Andersson G, Lindahl G, Hedén LO.
    Journal: J Immunol; 1994 Oct 15; 153(8):3557-64. PubMed ID: 7930578.
    Abstract:
    Cell surface proteins that bind to the Fc part of human IgA are expressed by different species of pathogenic streptococci. The most extensively characterized streptococcal IgA-binding protein is the Streptococcus pyogenes protein Arp4, a member of the M protein family. Here we describe work that identifies the IgA-binding region in this streptococcal protein. A comparison of the amino acid sequences of protein Arp4 and four other IgA-binding proteins of S. pyogenes first made possible the identification of a putative IgA-binding region. Site-specific mutagenesis and generation of deletions were then used to show that Arp4 derivatives lacking different parts of the putative IgA-binding region had lost the ability to bind IgA. Conclusive evidence for the localization of the IgA-binding region was obtained through the characterization of a chimeric protein, in which the putative IgA-binding region of Arp4 had been introduced into another S. pyogenes cell surface protein that does not bind IgA. Our data show that a region comprising 29-amino acid residues in the N-terminal part of Arp4 is necessary and sufficient for IgA-binding capacity. Competitive inhibition experiments with synthetic peptides indicated that the C-terminal half of this 29 residue region may be most important for the IgA-binding property of Arp4. These results identify, for the first time, the ligand-binding region in an Fc alpha binding protein.
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