SALS-WH2 inhibits actin assembly.
A, representative polymerization kinetics of actin (2.5 μm, containing 5% pyrenyl-actin) in the absence and presence of increasing amounts of SALS-WH2, as indicated. a.u., arbitrary units. B, rate of actin assembly determined from the initial slope of the pyrenyl traces as a function of SALS-WH2 concentration. Dashed line corresponds to the fit of the data using Equation 4, and the fit gave half-inhibition at 0.24 ± 0.1 μm SALS-WH2. Error bars, standard deviation. C, left panel, representative montages of TIRFM movies of actin assembly (0.5 μm, containing 10% Alexa488NHS-actin) recorded in the absence and presence of SALS-WH2 (0.59 μm), as indicated. Scale bar, 10 μm, elapsed time = min/s, look-up table: fire. Right panel, SALS-WH2 concentration dependence of the elongation rate of actin filaments, derived from TIRFM experiments. Dashed line corresponds to the fit of the data using Equation 4, and the fit gave half-inhibition at 0.38 ± 0.3 μm SALS-WH2. Error bars, standard deviation. D, representative polymerization kinetics of actin assembly from gelsolin/actin (GA2) seeds (1.5 μm, containing 5% pyrenyl-actin, [GA2] = 33 nm) in the absence and presence of increasing amounts of SALS-WH2, as indicated.