Table I.

Kinetic parameters for the two bound-state catch bond for T12 vinculin (top) and Vt (bottom). State 0 is the unbound state. States 1 and 2 are the weak and strong binding states, respectively. Each parameter is assigned a 95% confidence interval (in brackets) obtained through a parametric bootstrapping method in which 1000 simulated datasets were generated from the fitted model and parameters of best fit for each dataset were obtained through maximum likelihood estimation (17). Transition rate from state i to state j in the absence of load is indicated by k_ij. The application of load alters the equilibrium between state i and state j according to a distance parameter x_ij, which can be positive or negative, indicating that the transition rate is increased or decreased by force, respectively. These distance parameters vary depending on whether force is oriented toward the barbed (+) end or pointed (−) end of the actin filament.

Transition	kij0 (1/s)	CI (1/s)	xij (nm) pointed (−) end direction	CI (nm)	xij (nm) barbed (+) end direction	CI (nm)
1→ 0	5.3	[3.7, 7.6]	0	[0, 0.001]	0	[0, 0.1]
2→ 0	5.5 × 10−3	[0.0054, 0.0059]	1.2	[1.1, 1.2]	1.8	[1.7, 1.8]
1→ 2	6.1	[4.5, 9.4]	0.4	[0.4, 0.5]	0	[0, 0.003]
2→ 1	43	[39, 52]	−3.4	[−3.6, −3.4]	−1.6	[−1.7, −1.6]

Transition	kij0 (1/s)	CI (1/s)	xij (nm) pointed (−) end direction	CI (nm)	xij (nm) barbed (+) end direction	CI (nm)
1→ 0	3.9	[3.3, 4.8]	0	[0.0, 0.1]	0.5	[0.3, 0.5]
2→ 0	0.045	[0.027, 0.058]	0.3	[0.2, 0.5]	0.7	[0.7, 0.9]
1→ 2	2.7	[1.5, 3.5]	0	[0, 0.1]	0	[0, 0.02]
2→ 1	8.3	[3.3, 14.9]	−3.8	[−4.5, −2.9]	−2.8	[−3.6, −1.9]