FIGURE 4.

Mechanical strengths of CEC1-5 bonds. (A) Histogram of CEC1-5 versus CEC1-5 rupture forces measured under a steady ramp of 68 ± 5 pN/s. The solid lines are the probability distributions for the small fraction (∼30%) of rupture events attributed to the bound states measured between CEC12 fragments: namely, the orange line corresponds to the bound state with F_β = 5.2 and k_off = 3.9 s⁻¹, and the green line corresponds to the bond with F_β = 5.3 and k_off = 0.02 s⁻¹. The blue and red solid curves correspond to the stronger bound states exhibited by CEC1-5. (B) The most probable rupture force corresponding to the prominent peak in the CEC1-5 force histograms versus the logarithm of the loading rates. (C) Force histogram measured during the jump phase (4103 ± 591 pN/s) in the jump/ramp measurements. The majority of bonds (∼60%) survived the jump and failed during the ramp phase (7.8 ± 0.9 pN/s) shown in D. The corresponding histogram shows two, resolved peaks. The peak described by the blue curve is the same as the peak exhibiting the linear dependence shown in A. The second peak was fit by the probability distribution shown by the red curve. The bond parameters pertaining to the red and blue distributions are given in the text and summarized in Table 1.