RNA-protein interactions govern gene expression, viral replication, and cellular signaling. These interactions happen in a mechanical environment — ribosomes pull on mRNA, molecular motors generate tension, cytoskeletal forces deform the cell. But binding kinetics are usually measured in solution, where mechanical force is zero.
The authors (arXiv:2603.22269) model how external forces alter RNA-protein binding. The force tilts the energy landscape: pulling on the complex lowers the barrier to unbinding and raises the barrier to binding. The binding rate decreases and the unbinding rate increases — both exponentially in the force.
The exponential force dependence means small forces have large effects on binding equilibrium. A piconewton of force can shift the equilibrium constant by an order of magnitude. In cellular contexts where piconewton forces are routine (motor proteins, polymerase translocation, ribosomal ratcheting), the force contribution to binding dynamics is not a perturbation — it's a dominant term.
The through-claim: RNA-protein binding constants measured in solution are equilibrium properties of a system that, in vivo, is never at equilibrium. The forces present in the cell shift binding affinities by orders of magnitude. The “binding constant” is constant only in the absence of force — and force is never absent in the living cell.