Binding of Staphylococcus aureus Protein A to von Willebrand Factor Is Regulated by Mechanical Force

Binding of Staphylococcus aureus to the large plasma glycoprotein von
Willebrand factor (vWF) is controlled by hydrodynamic flow conditions. Currently, we
know little about the molecular details of this shear-stress-dependent interaction.
Using single-molecule atomic force microscopy, we demonstrate that vWF binds to
the S. aureus surface protein A (SpA) via a previously undescribed force-sensitive
mechanism. We identify an extremely strong SpA-vWF interaction, capable of withstanding
forces of 2 nN, both in laboratory and in clinically relevant methicillinresistant
S. aureus (MRSA) strains. Strong bonds are activated by mechanical stress,
consistent with flow experiments revealing that bacteria adhere in larger amounts to
vWF surfaces when the shear rate is increased. We suggest that force-enhanced adhesion
may involve conformational changes in vWF. Under force, elongation of vWF
may lead to the exposure of a high-affinity cryptic SpA-binding site to which bacteria
firmly attach. In addition, force-induced structural changes in the SpA domains
may also promote strong, high-affinity binding. This force-regulated interaction
might be of medical importance as it may play a role in bacterial adherence to
platelets and to damaged blood vessels.