The binding force of the staphylococcal adhesin SdrG is remarkably strong

SdrG is a cell surface adhesin from Staphylococcus epidermidis which binds to the blood plasma protein fibrinogen (Fg). Ligand binding follows a 'dock, lock and latch' model involving dynamic conformational changes of the adhesin that result in a greatly stabilized adhesin-ligand complex. To date, the force and dynamics of this multistep interaction are poorly understood. Here we use atomic force microscopy (AFM) to unravel the binding strength and cell surface localization of SdrG at molecular resolution. Single-cell force spectroscopy shows that SdrG mediates time-dependent attachment to Fg-coated surfaces. Single-molecule force spectroscopy with Fg-coated AFM tips demonstrates that the adhesin forms nanoscale domains on the cell surface, which we believe contribute to strengthen cell adhesion. Notably, we find that the rupture force of single SdrG-Fg bonds is very large, similar to 2 nN, equivalent to the strength of a covalent bond, and shows a low dissociation rate, suggesting that the bond is very stable. The strong binding force, slow dissociation and clustering of SdrG provide a molecular foundation for the ability of S. epidermidis to colonize implanted biomaterials and to withstand physiological shear forces.