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Vimentin-cross-reactive epitope of type 12 streptococcal M protein
W Kraus1, J M Seyer, E H Beachey
1Veterans Administration Medical Center, Memphis, Tennessee.
Abstract:
The NH2-terminal amino acid sequence of type 12 M protein was determined by automated Edman degradation of a 38-kilodalton polypeptide fragment purified from a limited pepsin digest of intact type 12 streptococci. The sequence of the first 13 amino acid residues of the polypeptide confirmed that predicted by the nucleotide sequence of the mature type 12 M protein. A chemically synthesized peptide copying the NH2-terminal 25 residues, SM12(1-25)C, evoked opsonic antibodies against type 12 streptococci as well as renal glomerular cross-reactive antibodies. The serum from one of six rabbits reacted in immunofluorescence tests with human glomeruli in a mesangial staining pattern. The cross-reactive antibodies were completely inhibited by the immunizing peptide and absorption with type 12 streptococci. Subpeptides of the 25-residue synthetic peptide were without inhibitory effect, suggesting that the cross-reactive antibodies are directed against a conformational epitope of SM12(1-25)C. Anti-SM12(1-25)C antisera reacted specifically with the intermediate filament protein vimentin extracted from mesangial cells. None of the cross-reactions of anti-SM12(1-25)C were inhibited by a synthetic peptide SM1(1-26)C of type 1 M protein, which was previously shown to share a cross-reactive epitope with vimentin. These results indicate that type 12 M protein contains at least one vimentin cross-reactive epitope that is clearly distinct from the tetrapeptide epitope shared with vimentin by type 1 M protein.
Insights
The NH2-terminal sequence of type 12 M protein was determined, revealing a distinct vimentin cross-reactive epitope. This epitope differs from that found in type 1 M protein, suggesting unique pathogenic mechanisms for type 12 streptococci.
Area of Science:
- Microbiology
- Immunology
- Protein Chemistry
Background:
- Streptococcus pyogenes type 12 M protein is a virulence factor.
- M proteins can share epitopes with host proteins, potentially leading to autoimmune complications like glomerulonephritis.
- Previous studies identified a shared epitope between type 1 M protein and vimentin.
Purpose of the Study:
- To determine the NH2-terminal amino acid sequence of type 12 M protein.
- To investigate the potential for cross-reactivity between type 12 M protein and human glomerular proteins, specifically vimentin.
- To characterize the epitope(s) responsible for cross-reactivity.
Main Methods:
- Automated Edman degradation was used to sequence a fragment of type 12 M protein.
- A synthetic peptide (SM12(1-25)C) corresponding to the N-terminus was synthesized.
- Antibodies were generated against the synthetic peptide and tested for cross-reactivity with human glomeruli and vimentin using immunofluorescence and inhibition assays.
Main Results:
- The determined N-terminal sequence matched the predicted sequence.
- SM12(1-25)C evoked opsonic and cross-reactive antibodies against human glomeruli.
- These cross-reactive antibodies specifically recognized vimentin and were directed against a conformational epitope distinct from the one shared by type 1 M protein.
Conclusions:
- Type 12 M protein possesses a unique vimentin cross-reactive epitope.
- This epitope is conformation-dependent and distinct from the previously identified epitope shared by type 1 M protein and vimentin.
- These findings contribute to understanding the pathogenesis of post-streptococcal glomerulonephritis and autoimmune cross-reactivity.