Stretching and twisting of double-stranded RNA under forces: Unwinding mechanism and base-pair dependent elasticity

We used all-atom molecular dynamics simulations to investigate the mechanical response of double-stranded RNA (dsRNA) by applying various forces. We used the helical rise and helical twist, as well as a newly defined helical diameter, to characterize the stretching and twisting of dsRNA. The results indicate that dsRNA unwinds when stretched, accompanied by a linear increase in helical rise and helical diameter. Then, we utilized the normal modes, which are linear combinations of helical modes, to elucidate the underlying mechanism of dsRNA unwinding from an energetic perspective. On the other hand, we employed a stiffness matrix based on a rigid base pair model to examine the base-pair dependence of twist elasticity for dsRNA, as well as stretch elasticities with respect to the helical rise and helical diameter. The results show that the force induces variations in the local elasticities and their couplings of dsRNA, which are closely related to the distributions of base pairs. The mean stretch and twist elasticities can be considered as constants within the measurement uncertainties; however, their couplings demonstrate a slight linear dependency on applied force.