Cells under Pressure
Cells in our body are exposed to a wide range of mechanical forces: they are under pressure or have to cope with shear and stretch. The goal of Carsten Grashoff and his research group is to understand the effects of these forces on cells in more detail. He therefore developed a microscopy method to measure forces across distinct proteins in cells.
Help came from an unexpected source –a spider. the golden silk spider Nephila clavipes is widespread on the American continent. The animals produce an extraordinarily tear-resistant and elastic fiber, which is already being tested as a raw material for textiles and safety belts. Grashoff used one component of the “miracle silk” in his research: the highly elastic protein flagelliform, which can be stretched by very little forces.
The Grashoff method is based on a physical effect called FRET (Förster Resonance Energy Transfer), which can occur between two different fluorescent molecules. If close to each other energy can be transferred form one molecule to the other causing it to emit light. By fusing two fluorescent molecules with the spider protein flagelliform, Grashoff generated a force-sensitive FRET probe that allows him to determine the tension on the linker flagelliform. By genetically incorporating this force sensor into protein extremely small forces can be measured.
Molecular power play
The first application used the protein vinculin, which is located at the plasma membrane of cells and important for surface adhesion during cell migration. Using his new method, Grashoff was able to show that not all vinculin molecules are stressed equally during cell migration: only molecules that lie in the direction of migration are exposed to force – the rest of the molecules can remain completely relaxed.