Pilus-1 Backbone Protein RrgB of Streptococcus pneumoniae Binds Collagen I in a Force-Dependent Way

Area of Science:

• Microbiology
• Biophysics
• Materials Science

Background:

• Pathogenic bacteria require attachment to host tissues for colonization and invasion.
• Pili, surface appendages on bacteria, mediate firm attachment to host surfaces.
• The RrgB protein's D3 domain in Streptococcus pneumoniae pili was hypothesized to mediate bacterial-host interactions, but previous studies found no affinity to collagen I.

Purpose of the Study:

• To investigate the interaction between the RrgB protein and human collagen I under mechanical load.
• To characterize the force-dependent binding properties of RrgB to collagen I.
• To determine if RrgB exhibits catch-bond behavior.

Main Methods:

• Atomic force microscopy-based single molecule force spectroscopy.
• Lateral force microscopy.
• Mechanical load application and shearing rate manipulation.

Main Results:

• RrgB binds to human collagen I in a force-dependent manner.
• Interaction forces reached up to 1500 pN, demonstrating exceptionally strong binding.
• High force loading and shearing rates enhanced and strengthened the RrgB-collagen I interaction.
• Binding affinity depended on the orientation of the RrgB D3 domain and collagen fibrils.

Conclusions:

• RrgB exhibits catch-bond behavior, characterized by force-induced strengthening of the interaction with collagen I.
• This is the first report of catch-bond behavior in multimeric backbone subunits of virulence-related pili.
• The findings reveal a novel mechanism for enhanced bacterial adhesion to host tissues mediated by pili under mechanical stress.