Figure 3.

Mechanical properties of C2A. (A) Two examples of force-extension curves obtained after stretching I27₂-C2A-I27₂ proteins. The thin lines correspond to fits to the WLC equation. In the example shown on the right, the C2A force peak precedes a low force peak. (B) Histogram of increases in contour lengths measured for the C2A domain. Most domains unfold in an all-or-none fashion in which the ΔL_c is ∼40nm (39.6 ± 4.5 nm, n = 51). However, we also observed ∼38% (31 of 82 recordings) of domains unfolded through an intermediate, which contributes to an increase in contour length of ∼7 nm (7.4 ± 3.5 nm, n = 31; blue bars). (C) An unfolding force histogram shows that C2A domains have unfolding forces of 51 ± 14 pN (n = 78).