Peter Bieling (Max-Planck-Institute of Molecular Physiology)
All eukaryotic cells actively establish and change their shape through a spatially diversified actin cytoskeleton. I will highlight current and new directions in our work on the cellular control of actin assembly. We recently reconstituted actin filament assembly from physiological actin concentrations, which showed how core actin regulators such as profilin and formin collaborate to pace the rate of filament growth independent of fluctuating concentrations of soluble actin in cells. This explains why actin dynamics in vivo can be both robust towards changes in global actin expression levels, but remain adaptable depending on regulatory activity. By overcoming the obstacles to the structural characterization of actin filament ends, we determined the first structures of actin end-binding proteins such as formins at their site of activity. This allowed us to uncover the molecular mechanism by which formins bind to, move with and control the speed of subunit addition at the actin filament end.