Maturation of siRNA by strand separation: Steered Molecular dynamics study

TL;DR

This study uses steered molecular dynamics simulations to explore the pathway and forces involved in the separation of siRNA strands, providing insights into the molecular mechanism of RNA interference.

Contribution

First computational analysis of siRNA strand separation pathway using steered molecular dynamics, revealing force requirements and potential biological mechanisms.

Findings

High force needed to pull one strand along the helix axis.

Intermediate force required for perpendicular strand separation.

Initial bubble formation requires high nucleation energy.

Abstract

RNA interference, particularly siRNA induced gene silencing is becoming an important avenue of modern therapeutics. The siRNA is delivered to the cells as short double helical RNA which becomes single stranded for forming the RISC complex. Significant experimental evidence is available for most of the steps except the process of the separation of the two strands. We have attempted to understand the pathway for double stranded siRNA (dsRNA) to single stranded (ssRNA) molecules using steered molecular dynamics simulations. As the process is completely unexplored we have applied force from all possible directions restraining all possible residues to convert dsRNA to ssRNA. We found pulling one strand along helical axis direction restraining far end of the other strand demands excessive force for ssRNA formation. Pulling a central residue of one strand, in a direction perpendicular to the helix axis, while keeping the base paired residue fixed requires intermediate force for strand separation. Moreover we found that in this process the force requirement is quite high for the first bubble formation (nucleation energy) and the bubble propagation energies are quite small. We hypothesize this could be the mode of action adopted by the proteins in the cells.