Serum opacity factor is a streptococcal receptor for the extracellular matrix protein fibulin-1

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Bacterial adhesion to host tissues is critical for infection.
• Extracellular matrix proteins are key targets for bacterial attachment.
• Streptococcus pyogenes utilizes various surface proteins to interact with host components.

Purpose of the Study:

• To investigate the interaction between Streptococcus pyogenes and the extracellular matrix protein fibulin-1.
• To identify the specific bacterial factors involved in fibulin-1 binding.
• To elucidate the functional significance of this interaction in bacterial adhesion.

Main Methods:

• Dose-dependent binding assays using purified fibulin-1 and S. pyogenes.
• Genetic manipulation of Streptococcus pyogenes to ablate serum opacity factor (SOF).
• Use of recombinant SOF peptides and domain mapping to identify binding sites.
• Mixed binding experiments to assess complex formation.

Main Results:

• S. pyogenes demonstrated dose-dependent binding to fibulin-1.
• Ablation of SOF reduced fibulin-1 binding by approximately 50%.
• Fibulin-1 bound to SOF with high affinity (K(d) = 1.6 nm), with a distinct binding domain separate from the fibronectin-binding domain.
• Fibulin-1 binding was observed across multiple S. pyogenes M types, suggesting conservation of the SOF-fibulin-1 interaction.
• A quaternary complex involving gelatin, fibronectin, fibulin-1, and SOF enhanced fibulin-1 binding.

Conclusions:

• Streptococcus pyogenes interacts with fibulin-1, with SOF being a major, but not exclusive, receptor.
• The SOF-fibulin-1 interaction is likely conserved across different S. pyogenes serotypes.
• These interactions may play a significant role in the adhesion of S. pyogenes to host extracellular matrices, contributing to pathogenesis.