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A two-domain mechanism for group A streptococcal adherence through protein F to the extracellular matrix
1The Hebrew University-Hadassah Medical School, Jerusalem 91010, Israel.
Abstract:
Streptococcus pyogenes binds to the extracellular matrix (ECM) and a variety of host cells and tissues, causing diverse human diseases. Protein F, a S.pyogenes adhesin that binds fibronectin (Fn), contains two binding domains. A repeated domain (RD2) and an additional domain (UR), located immediately N-terminal to RD2. Both domains are required for maximal Fn binding. In this study, we characterize RD2 and UR precisely and compare their functions and binding sites in Fn. The minimal functional unit of RD2 is of 44 amino acids, with contributions from two adjacent RD2 repeats flanked by a novel 'MGGQSES' motif. RD2 binds to the N-terminal fibrin binding domain of Fn. UR contains 49 amino acids, of which six are from the first repeat of RD2. It binds to Fn with higher affinity than RD2, and recognizes a larger fragment that contains fibrin and collagen binding domains. Expression of UR and RD2 independently on the surface-exposed region of unrelated streptococcal protein demonstrates that both mediate adherence of the bacteria to the ECM. We describe here a mechanism of adherence of a pathogen that involves two pairs of sites located on a single adhesin molecule and directed at the same host receptor.
Insights
Streptococcus pyogenes uses Protein F to adhere to host tissues by binding fibronectin (Fn). Two domains, RD2 and UR, within Protein F mediate this bacterial adherence to the extracellular matrix (ECM).
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Streptococcus pyogenes is a pathogen that causes various human diseases by adhering to host cells and tissues.
- Protein F is a key adhesin in S. pyogenes, responsible for binding to fibronectin (Fn), a component of the extracellular matrix (ECM).
- Protein F possesses two distinct binding domains, RD2 and UR, both crucial for efficient Fn binding.
Purpose of the Study:
- To precisely characterize the functions and binding sites of the RD2 and UR domains of Protein F within fibronectin.
- To elucidate the mechanism by which these domains contribute to bacterial adherence to the ECM.
Main Methods:
- Detailed biochemical characterization of the RD2 and UR domains, including determination of minimal functional units and amino acid composition.
- Affinity and binding site analysis of RD2 and UR interactions with fibronectin fragments.
- Functional expression of RD2 and UR on unrelated streptococcal proteins to assess their role in bacterial adherence.
Main Results:
- The minimal functional unit of RD2 comprises 44 amino acids, binding to the N-terminal fibrin-binding domain of Fn.
- The UR domain (49 amino acids) binds Fn with higher affinity, recognizing a larger fragment including fibrin and collagen-binding domains.
- Both RD2 and UR independently mediate bacterial adherence to the ECM when expressed on the bacterial surface.
Conclusions:
- Protein F utilizes two distinct domains, RD2 and UR, to bind fibronectin, contributing to Streptococcus pyogenes adherence.
- The study reveals a novel mechanism of pathogen adherence involving multiple binding sites on a single adhesin targeting the same host receptor.
- Understanding these interactions is critical for developing strategies to combat S. pyogenes infections.