Sarah Köster

Abstract: Mechanical properties of eukaryotic cells are to a great part determined by the cytoskeleton, a composite biopolymer network composed of three filament systems – intermediate filaments, F-actin and microtubules – along with cross-linkers and molecular motors. Among the three filament types, Intermediate filaments are the most flexible and the most extensible ones, with an intriguing non-linear behavior. It has been shown previously that the presence of intermediate filaments in a cell has an influence on cell mechanics. Here we unravel different contributions to network properties and cell mechanics, such as the assembly kinetics and mechanical properties of the individual filaments (in particular at high strains), filament-filament interactions, and network rheology. To explain our experimental results on molecular grounds, we design models that include the strictly hierarchical build-up of the filaments (with multiple alpha-helical domains arranged in parallel) and non-equilibrium transitions between folded and un-folded states. Taken together experiments and modelling indicate that intermediate filaments serve as “safety belts” and shock absorbers” for the cell, thus avoiding damage at high, fast impact while maintaining flexibility (e.g. during cell motility).