1 research outputs found
Myosin and tropomyosin stabilize the conformation of formin-nucleated actin filaments
The conformational elasticity of the actin cytoskeleton is
essential for its versatile biological functions. Increasing
evidence supports that the interplay between the structural and
functional properties of actin filaments is finely regulated by
actin-binding proteins, however, the underlying mechanisms and
biological consequences are not completely understood. Previous
studies showed that the binding of formins to the barbed end
induces conformational transitions in actin filaments by making
them more flexible through long-range allosteric interactions.
These conformational changes are accompanied by altered
functional properties of the filaments. To get insight into the
conformational regulation of formin-nucleated actin structures,
in the present work we investigated in detail how binding
partners of formin-generated actin structures, myosin and
tropomyosin, affect the conformation of the formin-nucleated
actin filaments, using fluorescence spectroscopic approaches.
Time-dependent fluorescence anisotropy and temperature-dependent
Forster-type resonance energy transfer measurements revealed
that heavy meromyosin, similarly to tropomyosin, restores the
formin-induced effects and stabilizes the conformation of actin
filaments. The stabilizing effect of heavy meromyosin is
cooperative. The kinetic analysis revealed that despite the
qualitatively similar effects of heavy meromyosin and
tropomyosin on the conformational dynamics of actin filaments,
the mechanisms of the conformational transition is different for
the two proteins. Heavy meromyosin stabilizes the formin-
nucleated actin filaments in an apparently single-step reaction
upon binding, while the stabilization by tropomyosin occurs
after complex formation. These observations support the idea
that actin-binding proteins are key elements of the molecular
mechanisms that regulate the conformational and functional
diversity of actin filaments in living cells