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Type 1 M protein of Streptococcus pyogenes. N-terminal sequence and peptic fragments
Abstract:
Limited proteolysis of the surface of type 1 Streptococcus pyogenes by pepsin gives rise to fragment Pep M1 of Mr 20270 as the main product which covers the N-terminal part of the M protein. The amino acid sequence was determined of the N-terminal region of the M protein representing the most exposed part of the molecule on the surface fibrils of streptococcal cells, which seems to be very important for the differentiation of the individual serological types. The sequence differs from the homologous N-terminal sequences of types 5, 6 and 24, and shows a homology with sequences repeating in the chain of type 24. Fragment Pep M1 binds to fibrinogen; the absence of its 30 N-terminal amino acid residues, however, abolishes this interaction which is believed to play a role in the virulence of S. pyogenes.
Insights
Researchers identified a key fragment (Pep M1) of Streptococcus pyogenes type 1 M protein. This fragment binds to fibrinogen, a crucial interaction for bacterial virulence.
Area of Science:
- Microbiology
- Molecular Biology
- Immunology
Background:
- Streptococcus pyogenes is a significant human pathogen.
- M proteins are crucial surface virulence factors involved in serotype differentiation.
- Understanding M protein structure is key to developing novel therapeutics.
Purpose of the Study:
- To determine the amino acid sequence of the N-terminal region of type 1 Streptococcus pyogenes M protein.
- To investigate the interaction of M protein fragments with fibrinogen.
- To elucidate the role of specific M protein domains in bacterial virulence.
Main Methods:
- Limited proteolysis of Streptococcus pyogenes type 1.
- Purification and characterization of M protein fragment Pep M1.
- Amino acid sequencing of the N-terminal region.
- Fibrinogen binding assays.
Main Results:
- Pep M1, a 20,270 Mr fragment, was identified as the main product of pepsin digestion.
- The N-terminal sequence of Pep M1 was determined and found to be unique compared to types 5, 6, and 24, but homologous to repeating sequences in type 24.
- Pep M1 binds to fibrinogen, and this interaction is lost upon removal of the N-terminal 30 amino acid residues.
Conclusions:
- The N-terminal region of type 1 M protein is critical for fibrinogen binding.
- Fibrinogen binding mediated by the M protein likely contributes to Streptococcus pyogenes virulence.
- Sequence variations in M proteins may explain serological type differences.