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An IgA-binding peptide derived from a streptococcal surface protein
E Johnsson1, T Areschoug, J Mestecky
1Department of Laboratory Medicine, Lund University, Sölvegatan 23, S-223 62 Lund, Sweden.
Abstract:
Surface proteins that bind to the Fc part of human IgA are expressed by many strains of Streptococcus pyogenes, a major human pathogen. Studies of these proteins have been complicated by their size and by their ability to bind human plasma proteins other than IgA. Here, we describe a synthetic 50-residue peptide, derived from streptococcal protein Sir22, that binds human IgA but not any of the other plasma proteins known to bind to Sir22. The peptide binds serum IgA and secretory IgA and binds IgA of both subclasses. Evidence is presented that the peptide folds correctly both in solution and when it is immobilized and that it readily renatures after denaturation. Together, these data indicate that the peptide corresponds to a protein domain that binds IgA with high specificity. This is the first report of an IgA-binding domain that retains its properties in isolated form.
Insights
Researchers created a synthetic peptide from Streptococcus pyogenes protein Sir22 that specifically binds human immunoglobulin A (IgA). This IgA-binding peptide domain retains its function in isolation.
Area of Science:
- Microbiology
- Immunology
- Protein Chemistry
Background:
- Streptococcus pyogenes expresses surface proteins binding the Fc region of human immunoglobulin A (IgA).
- Studying these proteins is challenging due to their size and non-specific binding to other human plasma proteins.
- Sir22 is a known IgA-binding protein from Streptococcus pyogenes.
Purpose of the Study:
- To characterize a specific IgA-binding domain from Streptococcus pyogenes protein Sir22.
- To develop a smaller, more specific IgA-binding molecule for research.
Main Methods:
- Synthesis of a 50-residue peptide derived from Sir22.
- Binding assays using serum IgA, secretory IgA, and various human plasma proteins.
- Analysis of peptide folding, immobilization, and refolding properties.
Main Results:
- The synthetic peptide specifically binds human IgA, including serum and secretory IgA across both subclasses.
- The peptide does not bind other human plasma proteins known to interact with Sir22.
- The peptide demonstrates correct folding in solution and when immobilized, and readily renatures after denaturation.
Conclusions:
- The 50-residue peptide represents a functional IgA-binding domain of Sir22.
- This isolated peptide domain exhibits high specificity for human IgA.
- This is the first report of an IgA-binding domain retaining its properties in an isolated form.