I study how mechanical forces define and alter cellular behavior from a single molecule level to the more complex level of cellular sub-structures. One specific protein structure called coiled coil is often found at cellular locations that are exposed to mechanical forces as for example in intermediate filaments or in molecular motors. Quantifying the folding mechanics and the thermodynamic properties of this protein structure using single molecule force spectroscopy shows that it does not unwind due to physiologically occurring forces in the molecular motor kinesin. A thermodynamic equilibrium model that we developed allows now designing artificial coiled-coils with a desired stability profile, which could be used as non-toxic fluorescent force sensors in vitro.

 Hair-like cellular substructures called filopodia are known to exert forces to the cells’ surroundings. These structures serve the cell as sensory antennae, probing the mechanical and chemical properties of distant objects. This function can be hijacked by pathogens such as bacteria, to approach the host cell. We could show that the bacterium Shigella, but more generally contact with a passive bead can induce filopodial retraction simply via binding to its tip. Quantifying filopodial mechanics shows that the pulling force exerted by filopodia results predominantly from the retrograde flow in the cell cortex and is limited by few molecular links at the tip. I found first evidence that filopodial tips could serve as mechanosensors for the cell, allowing e.g. to sense the rigidity of the cellular environment. My experiments show that filopodia are a perfect model system to better understand how external mechanical signals are translated into cell internal biochemical signaling pathways.