Elucidation of the spatio-temporal regulated formation mechanism of cellular actin-based structures.

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In cells, the formation of actin structures is regulated by the interaction between actin regulatory proteins. Formin homology proteins (formins) play an essential role in the formation of actin stress fibers and yeast actin cables. A mammalian formin mDia1 rotates along the long-pitch helix of F-actin during processive actin elongation (helical rotation). Helical rotation may impose torsional force on F-actin in the opposite direction to the twisting of F-actin by an actin depolymerizing factor cofilin. In the present study, we revealed that helical rotation of mDia1 imposes torsional force on F-actin and enhances resistant against the cofilin binding and the filament severing activity of cofilin. In addition, an active mutant of mDia1 tethered to cellular structures through its N-terminal region induces the formation of F-actin resistant to actin disassembly. These results indicate that helical rotation of mDia1 functions as an antagonistic mechanism to the cofilin activity.