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Structure, function, and genetics of streptococcal M protein
V A Fischetti1, K F Jones, S K Hollingshead
1Rockefeller University, New York, New York 10021.
Abstract:
Streptococcal M protein is a coiled-coil fibrillar structure extending about 60 nm from the cell wall. From DNA sequencing of the M6 protein gene, it has been determined that the C-terminal end contains a membrane anchor and an adjacent cell wall stabilization domain, both of which are similar to C-terminal regions of surface proteins in other gram-positive organisms. Studies with monoclonal antibodies revealed that the C-terminal half of the protein is conserved among M proteins of different serotypes, whereas the N-terminal half varies. The M protein contains tandem repeats, which, through homologous recombination, are responsible for the observed size variation of the M proteins from different streptococcal strains. M protein size mutants occur in a laboratory-grown culture at a frequency of 1/2,000 colony-forming units. DNA sequence analysis of the M gene in size mutants derived from a single strain suggests that sequence changes which result from homologous recombination may play a role in the antigenic variation of M protein.
Insights
Streptococcal M protein
Area of Science:
- Microbiology
- Molecular Biology
- Immunology
Background:
- Streptococcal M protein is a key virulence factor.
- It forms a coiled-coil fibrillar structure on the bacterial cell surface.
- Its C-terminal region anchors to the cell wall and shares similarities with other Gram-positive surface proteins.
Purpose of the Study:
- To investigate the structural and genetic basis of Streptococcal M protein variation.
- To understand the role of tandem repeats and homologous recombination in M protein size and antigenic variation.
Main Methods:
- DNA sequencing of the M6 protein gene.
- Analysis of M protein size mutants.
- Monoclonal antibody studies to assess protein conservation and variation.
Main Results:
- The C-terminal half of M protein is conserved, while the N-terminal half varies among serotypes.
- Tandem repeats within the M protein gene are linked to size variation.
- Homologous recombination appears to drive both size and antigenic variation of M protein.
Conclusions:
- Homologous recombination involving tandem repeats is a primary mechanism for Streptococcal M protein size and antigenic variation.
- Understanding these mechanisms is crucial for developing effective vaccines and treatments against streptococcal infections.