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Cloning and expression of the gene for an immunoglobulin G Fc receptor protein from a group A streptococcus
Abstract:
DNA containing the 5' end of the M-12 structural gene was used as a probe in colony hybridizations in an attempt to clone the M-76 gene from an M-type 76 group A streptococcal strain. A single positive colony was detected, and Southern hybridization analysis of plasmid DNA isolated from this colony indicated that the insert DNA had homology to the 5' end of the M-12 structural gene. Subclones were constructed to define the limits of the M-76 gene, and sonicates of these subclones were reacted with M-76-specific antiserum in immunodiffusion. A sonicate of one subclone, JM83(pDH56), reacted strongly with the M-76-specific antiserum but also reacted with preimmune rabbit serum. Protein expressed from this subclone bound immunoglobulin from horse and pig, as well as human myeloma immunoglobulin G (IgG) representing all four subclasses and purified human IgG Fc fragments. This indicated that JM83(pDH56) expressed a protein with characteristics previously attributed to the IgG Fc receptor protein from group A streptococci. Western blot analysis indicated that the cloned IgG Fc receptor protein had a molecular weight of approximately 29,000. Binding studies showed that the Fc receptor gene is expressed by the M-type 76 strain from which it was cloned and by an M- variant.
Insights
Researchers cloned the M-76 gene from group A streptococci, identifying a novel immunoglobulin G Fc receptor protein. This protein, approximately 29,000 molecular weight, is expressed by the M-type 76 strain.
Area of Science:
- Microbiology
- Molecular Biology
- Immunology
Background:
- Group A streptococci possess surface proteins, including M proteins, that contribute to virulence.
- Understanding the genetic basis of streptococcal virulence factors is crucial for developing effective treatments.
Purpose of the Study:
- To clone and characterize the M-76 gene from an M-type 76 group A streptococcal strain.
- To identify and analyze the protein product of the M-76 gene and its functional properties.
Main Methods:
- Colony hybridization using a DNA probe for the M-12 gene.
- Southern hybridization to confirm DNA homology.
- Subcloning and immunodiffusion assays with M-76-specific antiserum.
- Western blot analysis and protein binding studies to characterize the expressed protein.
Main Results:
- Successfully cloned a gene fragment with homology to the M-12 gene, designated as the M-76 gene.
- A subclone, JM83(pDH56), expressed a protein that reacted with M-76-specific antiserum and preimmune rabbit serum.
- The expressed protein bound various immunoglobulins, including human IgG subclasses and Fc fragments, indicating it functions as an immunoglobulin G Fc receptor.
- Western blot analysis revealed a molecular weight of approximately 29,000 for the cloned Fc receptor protein.
- Expression of the Fc receptor gene was confirmed in the M-type 76 strain and an M- variant.
Conclusions:
- The M-76 gene encodes a novel immunoglobulin G Fc receptor protein in group A streptococci.
- This Fc receptor plays a role in bacterial evasion of the host immune system.
- The cloned gene and its product provide valuable tools for studying streptococcal pathogenesis and host-pathogen interactions.