Conformational changes in actin filaments induced by formin binding to the barbed end

Formins bind actin. laments and play an essential role in the regulation of the actin cytoskeleton. In this work we describe details of the formin-induced conformational changes in actin. laments by fluorescence-lifetime and anisotropy-decay experiments. The results show that the binding of the formin homology 2 domain of a mammalian formin (mouse mDia1) to actin. laments resulted in a less rigid protein structure in the microenvironment of the Cys(374) of actin, weakening of the interactions between neighboring actin protomers, and greater overall flexibility of the actin. laments. The formin effect is smaller at greater ionic strength. The results show that formin binding to the barbed end of actin. laments is responsible for the increase of flexibility of actin. laments. One formin dimer can affect the dynamic properties of an entire. lament. Analyses of the results obtained at various formin/actin concentration ratios indicate that at least 160 actin protomers are affected by the binding of a single formin dimer to the barbed end of a. lament.