Fig. 1.

The BFP and a test of mechanical strength between trans-bonded EC15 fragments. (a) Videomicrograph of the BFP with a pipette-pressurized red cell as a force transducer, labeled by a spring on the left. The 2-μm streptavidinated glass bead carrying cadherin proteins (shown as green pins) was attached to the previously biotinylated red cell as a probe tip; a 4-μm glass bead (on the right) also decorated with cadherin was used as a target (shown as red wedges). (b) Schematic illustration of cadherins linked to the microbeads and the labeling of modules (see Fig. 5 for gels showing the isolated fragments). The cadherin densities on both the BFP tip and target beads were kept very low so that bead–bead contact in1 mM Ca²⁺ would produce infrequent pairwise attachments. (c) A force vs. time trace obtained from pulling on a pairwise EC15 vs. EC15 attachment by retracting the target at constant speed. Formed during 0.1-sec touch, the attachment survived for ≈0.07 sec under the steady force ramp, breaking precipitously at ≈64 pN.