Unfolding protein with an atomic force microscope: Force-fluctuation induced non-exponential kinetics

We show that in experimental atomic force microscopy studies of the lifetime distribution of mechanically stressed folded proteins the effects of externally applied fluctuations can not be distinguished from those of internally present fluctuations. In certain circumstances this leads to artificially non-exponential lifetime distributions which can be misinterpreted as a signature of protein complexity. This work highlights the importance of fully characterizing and controlling external sources of fluctuation in mechanical studies of proteins before drawing conclusions on the physics at play on the molecular level.