Bonds between fibronectin and fibronectin-binding proteins on Staphylococcus aureus and Lactococcus lactis

Area of Science:

• Microbiology
• Biophysics
• Biochemistry

Background:

• Bacterial adhesion to host tissues and medical devices is a critical factor in infection pathogenesis.
• Fibronectin-binding proteins (FnBPs) on the surface of Staphylococcus aureus mediate interactions with host fibronectin, a key event in prosthetic device infections.

Purpose of the Study:

• To investigate the role of fibronectin-binding proteins A and B (FnBPA and FnBPB) from Staphylococcus aureus in the binding to fibronectin.
• To characterize the biophysical properties of the bonds formed between bacterial FnBPs and fibronectin.

Main Methods:

• Atomic force microscopy (AFM) was employed to measure single-molecule binding forces between fibronectin-coated probes and engineered strains of Staphylococcus aureus and Lactococcus lactis.
• Strains included those deficient in FnBPA/FnBPB, expressing only FnBPA, or expressing only FnBPB.
• Biomechanical modeling (wormlike chain model) and nonlinear regression analysis were used to analyze force-distance curves.

Main Results:

• Staphylococcus aureus strains expressing either FnBPA or FnBPB exhibited significantly increased binding frequency to fibronectin compared to a double mutant lacking both proteins.
• AFM revealed distinct force signatures indicative of parallel bond formation between fibronectin and bacterial FnBPs.
• Ectopic expression of FnBPA or FnBPB on Lactococcus lactis conferred fibronectin-binding capabilities similar to S. aureus.

Conclusions:

• Fibronectin-binding proteins A and B are necessary and sufficient for Staphylococcus aureus adhesion to fibronectin-coated surfaces.
• The binding involves the formation of parallel, covalent bonds with specific biomechanical properties.
• Understanding these interactions is crucial for developing strategies to prevent prosthetic device infections.