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Residues 20, 22, and 26 determine the subtype specificities of staphylococcal enterotoxins C1 and C2
T N Turner1, C L Smith, G A Bohach
1Department of Bacteriology and Biochemistry, University of Idaho, Moscow 83843.
Abstract:
Nonconserved residues of staphylococcal enterotoxin C1 (SEC1) were converted to their counterparts in SEC2. The mutants that resulted were examined for reactivity with monoclonal antibodies (MAbs). Substitution at position 20, 22, or 26 interfered with binding of an SEC1-specific MAb. SEC1 mutants with substitutions at all three positions reacted only with an SEC2-specific MAb. Antibody-binding patterns were not associated with isoelectric point differences. All mutants retained biological activity.
Insights
Researchers modified staphylococcal enterotoxin C1 (SEC1) to resemble SEC2. Key residue substitutions altered antibody binding, confirming specific regions dictate MAb reactivity while preserving biological function.
Area of Science:
- Microbiology
- Immunology
- Protein Chemistry
Background:
- Staphylococcal enterotoxins (SEs) are potent exotoxins produced by Staphylococcus aureus.
- Staphylococcal enterotoxin C (SEC) exists in several variants (e.g., SEC1, SEC2) with distinct antigenic properties.
- Understanding the structural basis of SEC variant antigenicity is crucial for diagnostics and therapeutics.
Purpose of the Study:
- To investigate the role of specific nonconserved residues in the antigenic differences between staphylococcal enterotoxin C1 (SEC1) and SEC2.
- To determine which amino acid substitutions are critical for reactivity with monoclonal antibodies (MAbs).
Main Methods:
- Site-directed mutagenesis was used to convert nonconserved residues of SEC1 to their SEC2 counterparts.
- The resulting SEC1 mutants were analyzed for their binding reactivity with SEC1-specific and SEC2-specific MAbs.
- Isoelectric points of the mutants were determined to assess potential charge-related effects on antibody binding.
Main Results:
- Amino acid substitutions at positions 20, 22, or 26 in SEC1 individually disrupted the binding of an SEC1-specific MAb.
- A mutant with substitutions at all three positions (20, 22, and 26) exhibited reactivity exclusively with an SEC2-specific MAb.
- The observed changes in antibody-binding patterns were not correlated with alterations in the isoelectric points of the SEC1 mutants.
- All engineered SEC1 mutants maintained their inherent biological activity, indicating functional conservation.
Conclusions:
- Specific nonconserved residues within SEC1, particularly at positions 20, 22, and 26, are critical determinants of its antigenic specificity.
- These substitutions directly influence the binding epitopes recognized by MAbs, differentiating SEC1 from SEC2.
- The study provides valuable structure-function insights into the immunogenicity of staphylococcal enterotoxins.