Engineering Approaches to Biomolecular Motors

Engineering Approaches to Biomolecular Motors: From in vitro to in vivo Friday Speaker Abstracts

Measuring Force and Viscoelasticity inside Living Cells Lene Oddershede . Niels Bohr Institute, Copenhagen, Denmark.

Much progress has been done in understanding the action of single molecules in vitro, where single parameters affecting the system can be tested one at a time. However, results obtained in vitro face the criticism that the conditions are too far from being physiologically relevant. Therefore, it is important to take the next step, namely to investigate the systems under in vivo conditions, inside the living organism. Optical tweezers are excellent tools for such investigations, because they allow for quantitative exploration of biological systems, both at the level of the single molecule, the cell, and the whole organism [1]. An optical trap can be used to measure forces and distances, however, such measurements are not trivial inside the living cell as the cytoplasm is viscoelastic and the normal calibration procedures, which rely on a purely viscous environment, cannot be used. Instead, in order to reliably measure forces inside a living cell, a combination of active and passive calibration must be employed. In the talk, an active- passive calibration procedure inside living cells will be demonstrated [2] and there will be examples of how to perform forces measurements and how to determine the viscoelastic landscapes inside living cells. Among these results, focus will be on embryonic stem cells, where optical tweezers measurements show that the mechanical properties of the cells’ cytoplasm correlate with the cells’ stage of differentiation. Also, there will be measurements of the force generated by filopodia while cells interact with their surroundings, this traction force being mediated by polymerization and helical buckling of actin inside the protruding filopodia of living cells [3]. [1] Oddershede, Nature Chemical Biology 8, 879 (2012) [2] Mas et al., Physical Biology 10, 046006 (2013) [3] Leijnse et al., PNAS 112, 136 (2015)

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