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Type M12 protein from Streptococcus pyogenes is a receptor for IgG3
D S Retnoningrum1, A Podbielski, P P Cleary
1Department of Microbiology, University of Minnesota, Minneapolis 55455.
Abstract:
Streptococcus pyogenes, serotype M12, was discovered to express a human IgG3 binding protein. Western blot analysis of partially purified M12 protein, exposed to IgG3 myeloma protein, showed that both M12 Ag and the receptor protein were the same apparent size. A lambda clone (lambda 4.1) containing the emm12 open reading frame expressed both the M12 Ag and the IgG3 binding protein. The emm12 open reading frame was amplified by the polymerase chain reaction and subcloned into the expression vector pJLA602. Based on Western blot analysis, one recombinant Escherichia coli (pD3) expressed M12 protein with IgG3 binding activity. This result confirmed that the M12 protein from strain CS24 is also an IgG3 receptor. Deletion analyses showed that a truncated M12 protein encoded by an internal PvuII fragment was sufficient for IgG3 binding activity. Further deletion studies suggested that the IgG3 binding domain was located in a 200 amino acid internal fragment containing two directly repeated sequences. Other experiments suggest that the receptor did not bind to the same IgG3 domain as that recognized by protein G. The M12 protein did not bind human IgG1, IgG2, IgG4, or Ig from several other animal species.
Insights
Streptococcus pyogenes M12 protein acts as a human IgG3 receptor. This study identified the specific IgG3 binding domain within the M12 protein, aiding in understanding bacterial immune evasion.
Area of Science:
- Immunology
- Microbiology
- Molecular Biology
Background:
- Streptococcus pyogenes is a significant human pathogen.
- Understanding bacterial immune evasion mechanisms is crucial for developing therapeutics.
Purpose of the Study:
- To identify and characterize the human IgG3 binding protein expressed by Streptococcus pyogenes serotype M12.
- To determine the specific domain responsible for IgG3 binding.
Main Methods:
- Western blot analysis was used to assess protein size and binding activity.
- Polymerase chain reaction (PCR) and subcloning were employed to express the M12 protein in Escherichia coli.
- Deletion analyses were performed to map the IgG3 binding domain.
Main Results:
- The M12 protein from Streptococcus pyogenes serotype M12 was confirmed to bind human IgG3.
- Recombinant expression in E. coli demonstrated the IgG3 binding activity of the M12 protein.
- Deletion studies localized the IgG3 binding domain to a 200 amino acid internal fragment.
Conclusions:
- The M12 protein of Streptococcus pyogenes functions as an IgG3 receptor.
- The identified binding domain is distinct from the Protein G binding site.
- This finding contributes to understanding how S. pyogenes evades the human immune system.