Figure 1. VopV_rep1 was an unstructured protein that demonstrated high affinity for F-actin.

(a) The repeating structure of VopV was composed of three patterns of repeat sequences. The VopV_rep1 sequence used in this study is shown below, and the residues are color-coded by their hydrophobicity (charged: green; polar: cyan; glycine: yellow; and hydrophobic: gray) to emphasize the high proportion of hydrophilic residues. (b) Circular dichroism analysis of VopV_rep1 revealed a typical random coil spectrum with a minimum peak at approximately 196 nm. (c), (d) The binding affinities of VopV_rep1 and phalloidin with cytoskeletal actin were analyzed using isothermal titration calorimetry. The dissociation constant (K_d) and binding stoichiometry (N) obtained by curve fitting analysis are shown in the inset. The binding pattern of VopV_rep1 (c, left) was similar to that of phalloidin (d, left). After the addition of VopV_rep1, phalloidin did not bind to actin (c, right), as was observed for the addition of VopV_rep1 to phalloidin-saturated actin (d, right).