Figure 5.

Calponin reduced the persistence length of single actin filaments. (A) Thermally fluctuating actin filaments were imaged and parameterized in terms of an angle, θ, and the filament arc length, s. (B) Representative raw image of a fluorescently labeled actin filament. Overlaid is the corresponding filament skeleton backbone used for parameterization and analysis. (C) The cosine correlation function was used to determine the persistence length. Shown are data from movies of two single actin filaments with (dotted line) and without (solid line) a fivefold molar excess of basic calponin. The persistence lengths were derived from the slope of the curves (Eq. 1). (D) Calponin reduced the persistence length of actin from 17.6 ± 0.7 μm to 7.7 ± 0.6 μm (p < 0.001). Error bars represent the mean ± SE.