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Fibronectin receptors from gram-positive bacteria: comparison of active sites
H J Joh1, K House-Pompeo, J M Patti
1Center for Extracellular Matrix Biology, Albert B. Alkek Institute of Biosciences and Technology, Texas A&M University, Houston 77030.
Abstract:
Many parasitic bacteria express fibronectin binding proteins that are located on the cell surface. These proteins may act as adhesins and mediate the adherence of the microorganisms to fibronectin-containing host tissues. The ligand binding sites in the fibronectin receptor proteins from Gram-positive bacteria are composed of unique 37-48 amino acid long motifs that are repeated 3-4 times. We have now expressed the ligand binding sites of fibronectin receptors from Staphylococcus aureus, Streptococcus dysgalactiae (two receptors), and Streptococcus pyogenes as recombinant proteins. The purified recombinant proteins have the expected molecular weights as indicated by electrospray mass spectroscopy although they migrate abnormally on SDS-PAGE. Each recombinant protein effectively inhibited the binding of 125I-labeled intact fibronectin or the N-terminal fibronectin domain to Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus pyogenes. The relative inhibitory potency of the different recombinant proteins was similar for all target bacteria and is reflected in their relative affinities for fibronectin. Synthetic peptides corresponding to the repeat units of the ligand binding site of the fibronectin receptor proteins were shown to inhibit the binding of the N-terminal fibronectin fragment to Streptococcus pyogenes cells. Together with amino acid sequence comparison, these data demonstrate that the repeat motif of the fibronectin receptor of Streptococcus pyogenes conforms to the consensus sequence previously reported for the Staphylococcus aureus receptor and to one of the Streptococcus dysgalactiae receptors (McGavin et al., 1993).
Insights
Researchers studied fibronectin receptors on bacteria like Staphylococcus aureus. They found that specific protein repeat motifs are key for bacterial adherence to host tissues, inhibiting bacterial binding.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Parasitic bacteria often possess cell-surface fibronectin-binding proteins (FnBPs) that mediate adherence to host tissues.
- FnBPs in Gram-positive bacteria feature repeated 37-48 amino acid motifs within their ligand-binding domains.
Purpose of the Study:
- To characterize the ligand-binding sites of fibronectin receptors from key bacterial pathogens.
- To investigate the role of conserved repeat motifs in bacterial adhesion to fibronectin.
Main Methods:
- Expression and purification of recombinant fibronectin receptor ligand-binding domains from Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus pyogenes.
- Inhibition assays using purified recombinant proteins and synthetic peptides to block fibronectin binding to bacterial cells.
- Electrospray mass spectrometry and SDS-PAGE for protein characterization.
Main Results:
- Purified recombinant proteins exhibited expected molecular weights but abnormal SDS-PAGE migration.
- Recombinant proteins and synthetic peptides effectively inhibited fibronectin binding to all tested bacterial species.
- Inhibitory potency correlated with bacterial affinity for fibronectin, suggesting conserved binding mechanisms.
Conclusions:
- The repeat motif in Streptococcus pyogenes fibronectin receptors shares consensus sequences with Staphylococcus aureus and Streptococcus dysgalactiae receptors.
- These conserved repeat motifs are crucial for bacterial adherence to fibronectin-containing host tissues.