Hierarchical molecular architecture renders intracellular vimentin a high-performance, shock-absorbing material.

The mechanical properties of eukaryotic cells are to a great extent determined by the cytoskeleton, a composite network of different filamentous proteins. Among these, intermediate filaments (IFs) are exceptional in their molecular architecture and mechanical properties. Here we directly record stress-strain curves of individual vimentin IFs using optical traps and atomic force microscopy. We find a strong loading rate dependence of the mechanical response, supporting the hypothesis that IFs could serve to protect eukaryotic cells from fast, large deformations. Our experimental results show different unfolding regimes, which we can quantitatively reproduce by an elastically coupled system of multiple two-state elements.

Intermediate filaments (IFs) constitute a sophisticated filament system in the cytoplasm of eukaryotes. They form bundles and networks with adapted viscoelastic properties and are strongly interconnected with the other filament types, microfilaments and microtubules. IFs are cell type specific and apart from biochemical functions, they act as mechanical entities to provide stability and resilience to cells and tissues. We review the physical properties of these abundant structural proteins including both in vitro studies and cell experiments. IFs are hierarchical structures and their physical properties seem to a large part be encoded in the very specific architecture of the biopolymers. Thus, we begin our review by presenting the assembly mechanism, followed by the mechanical properties of individual filaments, network and structure formation due to electrostatic interactions, and eventually the mechanics of in vitro and cellular networks. This article is part of a Special Issue entitled: Mechanobiology.

The Göttingen Series in Biophysics is intended as a collection of research monographs in biological physics, carried out at the Institute for X-Ray Physics at the University of Göttingen, and in the framework of related research networks and collaborations. The series covers topics from molecular to cellular biophysics, includes experimental, numerical then theoretical work and combines methods development and studies of complex biological systems. In most cases, the contributions are based on PhD theses. With this book series, we intend to promote the individual monographs by putting them into the larger context of the research field. We hope to be able to enhance the visibility of the research carried out here, and to encourage others to build on our findings, use our methods and advance the filed in a collaborative spirit.

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