The adhesion energy per area between DC-SIGNR and 5 mol % Man 9 GlcNAc 2 -DPPE monolayers is determined from the pull-off force F po at the minimum in the forceÀdistance curve D Adh ( Figure 2B ) and the DerjaguinÀM€ ullerÀToporov model. 28 At the position of bond rupture ( Figure 2B, D Adh ) , the surfaces jump out of contact (Figures 2 and 3 , right pointing arrows). There is no evidence of irreversible damage to the membranes due to, for example, lipid pull-out or the rupture of the NTAÀhexahistidine linkage. This would be evident in altered force curves measured at the same position after membrane separation, as documented previously. 31 In these studies, Biochemistry ARTICLE upon reapproach after detachment, the measured force curve, D J , and D C were unchanged (Figure 2 ). When separating the surfaces, D Adh and the pull-off force were similar within experimental error, even after as many as seven successive measurements at the same contact site. The average time between successive measurements was 10À15 min, which is too short for damaged membranes to heal 31 but more than sufficient to allow re-equilibration, as evidenced by the reversibility of the measurements. The reversibility is expected because this is a multivalent (number of bonds = 4) interaction, and the affinity of individual monomerÀglycan bonds is relatively low. Leckband et al. 31 showed that lipid pull-out occurs at receptorÀligand bond energies >∼15kT, which is much higher than the energies of the individual monomerÀglycan bonds. Each tetramer is also anchored to the membranes via four hexahistidine anchors.