CMCB Life Sciences Seminar: Prof. Dr. Sarah Köster, University of Göttingen, Institute for X-Ray Physics

Host: Stefan Diez (B CUBE)

Title: "How to be squishy and protective at the same time – the physics of biological matter"

Abstract: The tissues in our body have astonishingly varying mechanical and dynamic properties, that are perfectly adapted to their function: muscle cells actively contract, immune cells are highly motile, and cells in the skin or lung form stable, highly connected ensembles. Importantly, biological cells and tissues possess elastic, solid-like properties and viscous, liquid-like properties at the same time. These viscoelastic mechanics are to a great part determined by the cytoskeleton, a composite biopolymer network composed of three filament systems – intermediate filaments, actin filaments and microtubules – along with cross-linkers and molecular motors.

Intermediate filaments are more flexible and much more extensible than the other cytoskeletal filaments, including an intriguing non-linear behavior. Using optical tweezers, we have characterized the response to pulling of two types of intermediate filaments (vimentin and keratin) that play an important role in, e.g., cancer metastasis. We were able to model this response by taking into account the strictly hierarchical build-up of the filaments. This unique architecture consists of multiple alpha-helical domains arranged in parallel and non-equilibrium transitions between folded and un-folded states. Combining the experiments and the model we conclude 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. We also unravel distinctly different behaviors of keratin versus vimentin filaments, in line with their roles in stationary and motile cells, respectively.