Salt induced hierarchical morphology change of actin/polycation complexes

Masui, Tomomi; Shikinaka, Kazuhiro*; Koizumi, Satoshi; Kakugo, Akira*; Hashimoto, Takeji; Gong, J.*

Hierarchical structures of F-actin, an anionic polyelectrolyte, and PDMAPAA-Q, a synthetic linear cationic polyelectrolyte (polycation), complexes in KCl salt solutions have been examined over a wide range of length scales from nanometer to micrometer using a combination of ultra-small-angle neutron scattering technique and fluorescence microscopy. We found hierarchical condensation of actin/polycation complex composed of a superbundle of 10 micrometer, protobundle of 100 nanometer, and protofilament (F-actin) of nanometer. These structures are largely influenced by salt concentrations. With increase of salt concentration superbundle structure changes from globular to extended states, simultaneously, the regularity of F-actin inside the protobundle increased and protobundle size increased about ten times larger. Further increase of salt concentration brings the protobundle disassemble to single F-actin.