FIGURE 2.

Specific interaction between holo-Tf and purified TfR at pH 7.4 in PBS. (A) Typical retraction force curves recorded with a holo-Tf coated tip on a TfR functionalized mica. Vertical axis indicates cantilever deflections as a function of the cantilever-sample retraction distance. The first curve from the top shows no particular features, and the second curve from the top shows an unspecific tip-surface adhesion event. The other curves display specific unbinding events between holo-Tf and TfR, which can clearly be differentiated form unspecific adhesion. The vertical force jump of events allows access to the holo-Tf-TfR unbinding force. The unbinding length of an event is measured by the distance separating the force jump from the tip-sample contact point (represented by the kink on the left of the curve). (B) Force histogram of 389 unbinding events obtained after analysis of 1500 force curves. The mean unbinding force is 56 ± 7 pN, for a mean loading rate of 4.6 nN/s. The gray line is a fitting curve. (C) Unbinding-length distribution for the events plotted in B, showing a mean unbinding length of 44 ± 2 nm. The gray line is a Gaussian fit.