Force-Induced Strengthening of the Interaction between Staphylococcus aureus Clumping Factor B and Loricrin.

Yves F Dufrêne,David Alsteens,Claire Valotteau,Joan A Geoghegan,Simon Bernard,Matthew R Parsek,Pauline Vitry,Cécile Feuillie

doi:10.1128/mbio.01748-17

Abstract

ABSTRACTBacterial pathogens that colonize host surfaces are subjected to physical stresses such as fluid flow and cell surface contacts. How bacteria respond to such mechanical cues is an important yet poorly understood issue. Staphylococcus aureus uses a repertoire of surface proteins to resist shear stress during the colonization of host tissues, but whether their adhesive functions can be modulated by physical forces is not known. Here, we show that the interaction of S. aureus clumping factor B (ClfB) with the squamous epithelial cell envelope protein loricrin is enhanced by mechanical force. We find that ClfB mediates S. aureus adhesion to loricrin through weak and strong molecular interactions both in a laboratory strain and in a clinical isolate. Strong forces (~1,500 pN), among the strongest measured for a receptor-ligand bond, are consistent with a high-affinity “dock, lock, and latch” binding mechanism involving dynamic conformational changes in the adhesin. Notably, we demonstrate that the strength of the ClfB-loricrin bond increases as mechanical force is applied. These findings favor a two-state model whereby bacterial adhesion to loricrin is enhanced through force-induced conformational changes in the ClfB molecule, from a weakly binding folded state to a strongly binding extended state. This force-sensitive mechanism may provide S. aureus with a means to finely tune its adhesive properties during the colonization of host surfaces, helping cells to attach firmly under high shear stress and to detach and spread under low shear stress.

Highlights

Bacterial pathogens that colonize host surfaces are subjected to physical stresses such as fluid flow and cell surface contacts
We discover that the clumping factor B (ClfB)-loricrin interaction is enhanced under tensile loading, providing evidence that the function of an S. aureus surface protein can be activated by physical stress
We initially investigated the forces involved in the adhesion of whole bacteria to Lor by using single-cell force spectroscopy (SCFS; Fig. 1B, left)

Summary

Introduction

Bacterial pathogens that colonize host surfaces are subjected to physical stresses such as fluid flow and cell surface contacts. These findings favor a two-state model whereby bacterial adhesion to loricrin is enhanced through force-induced conformational changes in the ClfB molecule, from a weakly binding folded state to a strongly binding extended state This force-sensitive mechanism may provide S. aureus with a means to finely tune its adhesive properties during the colonization of host surfaces, helping cells to attach firmly under high shear stress and to detach and spread under low shear stress. The S. aureus surface protein clumping factor B (ClfB) binds to the squamous epithelial cell envelope protein loricrin, but the molecular interactions involved are poorly understood. Whether the adhesive properties of CWA proteins change in response to mechanical force is not known Solving this problem would help us understand how bacteria colonize mucosal surfaces while being subjected to various physical stresses, including fluid flow and cell surface interactions. Following the insertion of a short peptide sequence of Lor into a hydrophobic trench formed between the N2 and N3 subdomains of ClfB, a conformational change at the C terminus of N3 locks the peptide in place [12,13,14,15]

Methods

Results

Conclusion