Mechanical Stabilization of a Bacterial Adhesion Complex.

Area of Science:

• Microbiology
• Biophysics
• Biochemistry

Background:

• Gram-positive bacteria utilize adhesion complexes to bind host tissues.
• Tensile forces on these adhesions are variable and can influence binding strength.
• Previous studies lacked the technology to probe adhesion mechanics at physiologically relevant forces.

Purpose of the Study:

• To investigate the catch-bond kinetics of the SD-repeat protein G (SdrG) and fibrinogen β (Fgβ) adhesion complex.
• To determine the mechanical properties of bacterial adhesions under piconewton forces.
• To understand the role of mechanical forces in bacterial adhesion and pathogenesis.

Main Methods:

• Utilized an ultrastable magnetic tweezer-based single-molecule approach.
• Measured the lifetime of the SdrG-Fgβ complex under forces ranging from piconewtons to tens of pN at 37 °C.
• Analyzed the dissociation pathway of the adhesion complex.

Main Results:

• The lifetime of the SdrG-Fgβ complex exponentially increased with force, reaching ~1000 s at 30 pN.
• Demonstrated mechanical stabilization of the bacterial adhesion.
• Identified the unbinding of the SdrG "latch" strand as the critical dissociation step.
• Observed similar catch-bond kinetics in homologous bacterial adhesions.

Conclusions:

• Bacterial adhesions exhibit catch-bond kinetics, leading to mechanical stabilization under force.
• This force-dependent strengthening enhances bacterial adhesion and is likely crucial for pathogenesis.
• The findings suggest a general mechanism for bacterial adaptation and host colonization.