Mechanical Forces between Mycobacterial Antigen 85 Complex and Fibronectin.

Area of Science:

• Microbiology
• Biophysics
• Molecular Biology

Background:

• Bacterial adhesion to host extracellular matrix proteins is crucial for pathogen invasion.
• Mycobacterial Ag85 complex proteins mediate cell envelope synthesis and are known to bind fibronectin (Fn).
• The molecular forces governing the Ag85-Fn interaction remain largely uncharacterized.

Purpose of the Study:

• To investigate the strength, kinetics, and thermodynamics of the Ag85-Fn interaction.
• To focus on the multidrug-resistant Mycobacterium abscessus species.
• To elucidate the role of mechanical forces in Ag85-Fn binding.

Main Methods:

• Single-molecule force spectroscopy (SMFS) was employed to probe the Ag85-Fn interaction at the single-molecule level.
• Mechanical stress was applied to measure rupture forces and loading rate dependence.
• Thermodynamic parameters were extracted using the Friddle-Noy-de Yoreo theory.

Main Results:

• Single Ag85 proteins bind Fn with a force of approximately 75 pN under moderate tensile loading.
• Binding specificity was confirmed using specific peptides.
• Rupture force increased with mechanical stress, consistent with established biophysical models.
• Stronger bonds (up to 500 pN) were observed under high tensile loading.

Conclusions:

• The Ag85-Fn interaction is stress-sensitive, exhibiting increased bond strength under higher mechanical forces.
• These findings suggest a mechanism for robust mycobacterial attachment in high-shear environments like the lungs.
• The study provides novel insights into the function of Ag85 as a virulence factor and a stress-sensitive adhesin.