Figure 8:

(A) Schematic of a FRET-based tension sensor calibration experiment. Energy transfers from donor to acceptor dye on the end of a mechanosensitive protein when the ends are near each other. The length at a given force applied by optical tweezers can be correlated with the FRET efficiency. (B) Sketch of measured force-extension curves (to scale) for tension sensors HP35⁴⁹ and spider-silk peptides (GPGGA)_N.⁴⁶ Structures show possible configurations of HP35 commensurate with marked point on the force-extension curve taken from our preliminary MD simulations. The structure of the silk peptides under force in these experiments is not well understood.⁴⁶