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syn21679-sup-0001-suppfig1.tif2487KSupplementary Figure 1. General working principle of measuring binding activity on the single molecule level by AFM. Binding activity of cadherin fusion proteins covalently coupled to the tip and plate of the AFM are monitored by so-called force-distance cycles. As illustrated in the upper panel molecules are brought into contact and separation by cyclic up- and downward movements of the tip. When the tip hits the plate (3) the cantilever will be deflected upward until the end of the approach. During the retrace the cantilever bends back until the tip seperates from the plate. If during the contact phase the tip-bound cadherins interact specifically with the cadherins bound to the substrate, the cantilever will be deflected and will be pulled down below the neutral line during the separation phase (5), until a critical force is reached at which the cadherin bond breaks. Unbinding is followed by an abrupt jump of the cantilever to the neutral position (6). The degree and the frequency of deflection of the cantilever during several force-distance cycles are taken as a measure of the binding activity. The left lower panel shows a scheme of a force-distance cycle showing one specific cadherin-cadherin-interaction whereas the right lower panel shows original registrations of retrace curves of cadherin-interactions as well as of a control.

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