Localization of MSD in the juxtamembrane stalk region of GPIbα. (A) Overlaid force-distance traces of pulling VWF-A1 on GPIb-IX captured by biotinylated WM23 (red trace) and on GPIb-IX captured by biotin at the GPIX cytoplasmic domain (gray). (B) Plots of lifetimes of the GPIb-IX/VWF-A1 bond vs force (mean ± SEM, n >3).