Nanoscale Mechanics of FnBPB-Mediated Adhesion of Staphylococcus aureus to Skin Ligands

Staphylococcus aureus commonly colonizes human skin, impairing barrier integrity and increasing the risk of diseases such as atopic dermatitis (AD). The staphylococcal fibronectin-binding protein B (FnBPB) engages in attachment to the skin, yet little is known about the interaction mechanisms of its two functional regions: an N-terminal A domain responsible for fibrinogen-specific binding, and a C-terminal domain composed of fibronectin-binding repeats (FnBRs). Here, we combine atomic force microscopy with the use of isogenic S. aureus strains expressing wild-type FnBPB or domain-specific mutants to dissect the individual contributions of the A domain and FnBRs to two key skin ligands, fibrinogen (Fg) and fibronectin (Fn). Force spectroscopy with bacterial probes reveals that both functional regions play critical roles in mediating the adhesion of S. aureus to healthy and AD corneocytes. Force spectroscopy with Fg- or Fn-functionalized tips shows that FnBPB binds Fg via a stress-activated dock, lock, and latch (DLL) mechanism, with forces up to ∼2 nN, while Fn engages in both weak bonds (∼0.1 nN) and strong, force-dependent tandem β-zipper interactions (∼0.8 nN). In the absence of FnBRs, the lifetime and stability of Fg bonds are greatly reduced, suggesting this domain contributes to the bond stability. In addition, the A domain not only governs Fg DLL interaction but also assists Fn-binding. Collectively, our findings provide a biophysical foundation for the multifunctional adhesion properties of FnBPB during skin colonization, being able to bind multiple ligands using a complex synergy of interactions.