Localization of the equine IgG-binding domain in the fibrinogen-binding protein (FgBP) of Streptococcus equi subsp. equi.
Fibrinogen-binding protein (FgBP, also termed SeM) is a cell-wall-associated anti-phagocytic M-like protein of the equine pathogen Streptococcus equi subsp. equi, and binds fibrinogen (Fg) and IgG. FgBP binds Fg avidly through residues located at the extreme N terminus of the molecule, whereas the IgG-binding site is more centrally located between the A and B repeats. FgBP binds equine IgG4 and IgG7 subclasses through interaction with the CH2-CH3 interdomain region of IgG-Fc, and possesses overlapping Fc-binding sites with protein A and protein G. In this study, FgBP truncates containing defined internal deletions were used to identify a stretch of 14 aa (residues 335-348) critical for IgG binding. Protein chimeras consisting of the non-IgG-binding alpha-helical coiled-coil M5 protein fused to FgBP sequences were used to identify a minimal equine IgG-binding domain consisting of residues 329-360. Competition ELISA tests suggested that IgG does not compromise Fg binding and vice versa.
Meehan
Mary
M
Department of Microbiology, Moyne Institute of Preventative Medicine, Trinity College, Dublin 2, Ireland.
Lewis
Melanie J
MJ
Division of Medical Sciences, University of Dundee Medical School, Ninewells Hospital, Dundee DD1 9SY, UK.
Byrne
Caroline
C
Department of Microbiology, Moyne Institute of Preventative Medicine, Trinity College, Dublin 2, Ireland.
O'Hare
David
D
Department of Microbiology, Moyne Institute of Preventative Medicine, Trinity College, Dublin 2, Ireland.
Woof
Jenny M
JM
Division of Medical Sciences, University of Dundee Medical School, Ninewells Hospital, Dundee DD1 9SY, UK.
Owen
Peter
P
Department of Microbiology, Moyne Institute of Preventative Medicine, Trinity College, Dublin 2, Ireland.
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D005340:Fibrinogen / Q000378:metabolism; D006736:Horses; D007074:Immunoglobulin G / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018502:Streptococcus equi / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D007074:Immunoglobulin G; D011994:Recombinant Proteins; C112406:fibrinogen-binding protein, Streptococcus equi; D005340:Fibrinogen