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

Abstract

Binding ofStaphylococcus aureusto 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 theS. aureussurface 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 methicillin-resistantS. 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.IMPORTANCEStaphylococcus aureusprotein A (SpA) binds to von Willebrand factor (vWF) under flow. While vWF binding to SpA plays a role inS. aureusadherence to platelets and endothelial cells under shear stress, the molecular basis of this stress-dependent interaction has not yet been elucidated. Here we show that the SpA-vWF interaction is regulated by a new force-dependent mechanism. The results suggest that mechanical extension of vWF may lead to the exposure of a high-affinity cryptic SpA-binding site, consistent with the shear force-controlled functions of vWF. Moreover, strong binding may be promoted by force-induced structural changes in the SpA domains. This study highlights the role of mechanoregulation in controlling the adhesion ofS. aureusand shows promise for the design of small inhibitors capable of blocking colonization under high shear stress.

Next Generation Methods for Single-Molecule Force Spectroscopy on Polyproteins and Receptor-Ligand Complexes

“…For example, high-affinity non-covalent interactions including Ni:His-tag and Biotin:Avidin have both been used as immobilization tags onto surfaces or as the object of study in AFM-SMFS (Fritz et al, 1998;Berquand et al, 2005;Dupres et al, 2005;Li et al, 2019), as shown in Figure 1B. Many different classes of receptor-ligands have been probed by AFM (Milles et al, 2017;Liu et al, 2019), including antibody-antigen interactions (Dammer et al, 1996;Hinterdorfer et al, 1996Hinterdorfer et al, , 1998Allen et al, 1997;Ros et al, 1998;Schwesinger et al, 2000;Kienberger et al, 2005;Sulchek et al, 2005Sulchek et al, , 2006Neuert et al, 2006;Odorico et al, 2007;Morfill et al, 2008;Roy et al, 2010;Bizzarri and Cannistraro, 2014;Klamecka et al, 2015;Tsai et al, 2016;Liu et al, 2019Liu et al, , 2020, avidin systems (see below), bacterial adhesion systems (Herman et al, 2014;Schoeler et al, 2014;Jobst et al, 2015;Nash et al, 2016;Alonso-Caballero et al, 2018;Herman-Bausier et al, 2018;Milles et al, 2018;Viela et al, 2019), and others (Sletmoen et al, 2004;Farrance et al, 2013).…”

How Microbes Use Force To Control Adhesion

“…Such "catch" bonds ( 62) are proposed to exhibit longer lifetimes than their antonymous "slip" bonds, which is very useful to pathogens that need to stay adhered to their host-target tissues under hydrodynamic forces (58). AFM has provided evidence for the existence of catch bonds in ClfA, ClfB, and SpA (63)(64)(65), revealing that their binding strength is considerably increased by mechanical tension. The proposed mechanism involves force-induced conformational changes in the adhesins, from a weakly binding state to a strongly binding state, and explains how staphylococci can resist physical stresses such as hydrodynamic shear forces.…”

“…Another pertinent question is whether microbes express their adhesins homogenously or whether these form nanodomains capable of enhancing adhesion. FD-based imaging detected such clustering in S. aureus for various adhesins, including FnBPs, SdrG, ClfA, ClfB, SpA, and SpsL (48,64,69,70). It has been suggested that protein clustering on the cell surface may favor adhesion through multivalency.…”

What makes bacterial pathogens so sticky?

“…These results led to the conclusion that ClfA interacts with Fg via two distinct binding sites, whose adhesive function is regulated by mechanical tension. Lastly, mechanical tension also activated the adhesive function of SpA (Viela, Prystopiuk, et al, ). Under tensile loading, the adhesin binds to the large plasma glycoprotein von Willebrand factor with a force of ~2,000 pN.…”