Unfolding compactly folded molecular domains: Overall stiffness modifies the force-barrier relation

Using two different coarse-grained models, we show that the relation between force and energy barrier associated with domain unfolding in force-extension (length-control) experiments is highly sensitive to overall stiffness and therefore to the number of domains that already unfolded, the properties of the linker-molecule, and the stiffness of the experimental apparatus. Since the rate-dependent behavior of the molecule is dominated by energy barriers, our results suggest that the common assumption of barriers depending only on force may lead to erroneous interpretation of experiments. Further, recovering energy landscape from measurements of unfolding statistics must account for overall stiffness.