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Group G streptococcal IgG binding molecules FOG and protein G have different impacts on opsonization by C1q

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Author

Summary, in English

Recent epidemiological data on diseases caused by beta-hemolytic streptococci belonging to Lancefield group C and G ( GCS, GGS) underline that they are an emerging threat to human health. Among various virulence factors expressed by GCS and GGS isolates from human infections, M and M-like proteins are considered important because of their anti-phagocytic activity. In addition, protein G has been implicated in the accumulation of IgG on the bacterial surface through non-immune binding. The function of this interaction, however, is still unknown. Using isogenic mutants lacking protein G or the M-like protein FOG ( group G streptococci), respectively, we could show that FOG contributes substantially to IgG binding. A detailed characterization of the interaction between IgG and FOG revealed its ability to bind the Fc region of human IgG and its binding to the subclasses IgG1, IgG2, and IgG4. FOG was also found to bind IgG of several animal species. Surface plasmon resonance measurements indicate a high affinity to human IgG with a dissociation constant of 2.4 pM. The binding site was localized in a central motif of FOG. It has long been speculated about anti-opsonic functions of streptococcal Fc-binding proteins. The presented data for the first time provide evidence and, furthermore, indicate functional differences between protein G and FOG. By obstructing the interaction between IgG and C1q, protein G prevented recognition by the classical pathway of the complement system. In contrast, IgG that was bound to FOG remained capable of binding C1q, an effect that may have important consequences in the pathogenesis of GGS infections.

Publishing year

2007

Language

English

Pages

17530-17536

Publication/Series

Journal of Biological Chemistry

Volume

282

Issue

24

Document type

Journal article

Publisher

American Society for Biochemistry and Molecular Biology

Topic

  • Infectious Medicine

Status

Published

ISBN/ISSN/Other

  • ISSN: 1083-351X