How do ribozymes accommodate additional water molecules upon hydrostatic compression deep into the kilobar pressure regime?

Solvation by water plays an important role in the functional dynamics of biomacromolecules such as proteins or nucleic acids. This suggests that changes in solvation might drastically affect their functionality. Among other solvation stressors such as temperature, cosolvents or crowding agents, applying pressure in the multi-kilobar regime is known to modulate the hydration pattern of solutes, from simple to complex. In this study, we simulated a hairpin ribozyme, being catalytic RNA, using extensive replica-exchange molecular dynamics simulations at ambient and high hydrostatic pressure conditions. By dividing the coordinating water molecules present in the first solvation shell of the ribozyme into two subgroups, namely H-bonding and interstitial water, we discover that the H-bond network remains essentially unaffected even upon compression to 10 kbar compared to the 1 bar reference pressure. In stark contrast, the contribution of interstitial water significantly increases upon compression to 10 kbar, which discloses a differential effect of pressure perturbation on the solvation state of this ribozyme. In simple words: the increased water density due to compressing the aqueous ribozyme solution is locally accommodated by mainly pushing water molecules into the interstitial space offered by the existing H-bonding network of this RNA species. Given the molecularly generic nature of this finding, we expect it to hold true also for other biomacromolecules in aqueous solutions at high hydrostatic pressures, such as DNA or proteins.