Figure 5.

Analyzing the dynamics of the integrin conformational changes. (A,B) Mean ± SEM of the switching time (t_sw±, A) or time-to-switch (t_0±, B) averaged over all clamping forces. (C,D) Bending (open symbols) and unbending (filled symbols) t_sw± (C) or t_0± (D) vs. pre-switch force curves for indicated integrins (Mean ± SEM). In A-D, bending of D723R and L138I α_Vβ₃ occurred too infrequently to obtain sufficient data for statistically stable characterization thus were not summarized. (E) WT α_Vβ₃-FN_III7-10 lifetime vs. force data from measurements not containing bending and unbending events, to show the potential constraints of the receptor–ligand bond lifetime to the observable t_sw± (C) and t_0± (D). Lifetimes of WT α_Vβ₃ bonds with FN_III7-10 captured by monomeric SA (MT, blue) at 25 and 50 pN were compared to those by tetrameric SA (WT, magenta) over an entire force range. (F) Ratio of WT α_Vβ₃ time-to-unbend t₀₊ to time-to-bend t₀₋ vs. clamping force, showing the force-dependent bent/extended state equilibrium. The solid circles were calculated from data in panel D. The value of the open circle was the ratio of the extended to bent integrin sub-populations estimated from Fig. 4F. N.S. = not significant; * = p < 0.05; ** = p < 0.01; *** = p < 0.001 **** = p < 0.0001, assessed by unpaired, two-tailed Student’s t-test.