SUPRAMOLECULAR ASSEMBLIES |
Tensile properties of single desmin intermediate filaments
Laurent Kreplak 1*, Harald Herrmann 2 and Ueli Aebi 3
1 Dalhousie University
2 German Cancer Research Center
3 M.E. Muller Institute for structural biology
* To whom correspondence should be addressed. E-mail: kreplak{at}fizz.phys.dal.ca.
Submitted on August 21, 2007
Revised on September 27, 2007
Accepted on 28 November 2007
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Abstract |
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Within muscle fibers, desmin intermediate filaments (IFs) are major constituents of the extra-sarcomeric cytoskeleton. However, their contribution to the mechanical properties of myocytes has remained elusive. We present an experimental approach to measure the extensibility and the tensile strength of in vitro reconstituted desmin IFs adsorbed to a solid support. The tip of an atomic force microscope (AFM) was used to push on single filaments perpendicular to the filament axis. The torque of the AFM cantilever was monitored during the pushing events to yield an estimate of the lateral force necessary to bend and stretch the filaments. Desmin IFs were stretched up to 3.4 fold with a maximum force of ~3.5 nN. Fully stretched filaments exhibited a much smaller diameter than native IFs, i.e. ~3.5 nm compared to 12.6 nm, both by AFM and electron microscopy. Moreover, we combined the morphological and lateral force data to compute an average stress-strain curve for a single desmin filament. The main features were a pronounced strain-hardening regime above 50% extension and a tensile strength of at least 240 MPa. Because of these non-linear tensile properties, desmin IFs may dissipate mechanical energy and serve as a physical link between successive sarcomeres during large deformation.
Key Words:
atomic force microscopy, cytoskeleton, extensibility, intermediate filaments, mechanical stress, plasticity
