Structural and functional analysis of the human IgG-Fab receptor activity of streptococcal protein G.
Streptococcal protein G (SPG) shows specific binding activity to IgGs and serum albumins from various species. In order to investigate the structural domains of SPG responsible for the specific interaction with human IgG-Fab, the binding characteristics of a collection of recombinant receptors were analysed. The study includes receptors comprising different parts of the SPG molecule as well as chimeric receptors containing IgG-binding domains of staphylococcal protein A (SPA) fused to the N-terminal AB-region of SPG, which has been claimed to interact with human IgG-Fab. Purified defined gene products were allowed to compete for the binding to human IgG, human IgG-F(ab')2 fragments and human serum albumin (HSA) in several sets of competitive binding experiments. The results demonstrate that the C-terminal C domains have both IgG-Fc- and IgG-Fab-binding capacities, whereas the N-terminal AB region is responsible for the HSA-binding only. These results, which are in conflict with previous work, demonstrate that the binding to both the IgG-Fc and the IgG-Fab region is mediated by the same structurally distinct receptor region of SPG.
Department of Biochemistry and Biotechnology, Royal Institute of Technology, Stockholm, Sweden.
M
M
Eliasson
R
R
Andersson
P A
PA
Nygren
M
M
Uhlén
D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism*; D007074:Immunoglobulin G / Q000378:metabolism; D066298:In Vitro Techniques; D011971:Receptors, Immunologic / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D012709:Serum Albumin / Q000378:metabolism; D013205:Staphylococcal Protein A / Q000378:metabolism*; D013291:Streptococcus / Q000276:immunology; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; D012709:Serum Albumin; D013205:Staphylococcal Protein A