Fig. 4. Interaction of various PEVK fragments with actin. (A) In vitro acto-HMM velocity as a function of PPAK and pure polyE fragment concentration. The assay was carried out in the presence of 140 mM KCl. The data were normalized to the velocity in the absence of PEVK fragment (concentration=0 µg/ml), which was 3.2 µm/s for the PPAK fragment and 3.0 µm/s for the pure polyE fragment. (B) Solid-state surface binding of F-actin by PPAK and pure polyE fragments as a function of KCl concentration. The total filament length per field of view at the initial concentration of 25 mM KCl were 400 µm and 1140 µm for the PPAK and pure polyE fragments, respectively. (C) F-actin crosslinking assay in the presence of various PEVK fragments. (i) Actin filaments in the presence of PPAK. (ii) Crosslinked actin filaments in the presence of pure polyE fragment. Bar 20 µm. (iii) Summary of the actin-crosslinking assay.