FIG 5.

Mechanical activation of vWF binding to SpA. (A) Strength of single SpA-vWF bonds measured at increasing loading rates (LRs) on Newman WT bacteria (2,468 adhesive events from 6 cells). All adhesion peaks were analyzed to take into account all possible interactions. (B) Analysis of the data in panel A showing that strong bonds are favored at high LR. Discrete ranges of LRs were binned, and the forces were plotted as histograms (see Fig. S3 in the supplemental material). (C) Stiffness of the SpA-vWF complex (k_m) at low (<500 pN) and high (>500 pN) tensile forces. A cutoff of 500 pN was chosen as essentially all low adhesion forces at low stress were smaller than this value (see panel B). (D) Plot of k_m as a function of the adhesion force showing that the high mechanical stability of the bond correlates with a high molecular stiffness. (E and F) SpA-dependent bacterial adhesion to vWF increases with fluid shear stress. Shown are optical microscopy images of Newman WT and Δspa bacteria adhering to vWF-coated surfaces in a microparallel flow chamber under low and high shear stresses. Shown in panel F is the quantification of the amounts of adhering bacteria estimated from the experiments described in panel E from a total of 6 images from 3 experiments for each condition.