Rotational dynamics of proteins in nanochannels: role of solvent's local viscosity

Viscosity variation of solvent in local regions near a solid surface, be it a biological surface of a protein or an engineered surface of a nanoconfinement, is a direct consequence of intermolecular interactions between the solid body and the solvent. The current coarse-grained molecular dynamics study takes advantage of this phenomenon to investigate the anomaly in a solvated protein's rotational dynamics confined using a representative solid matrix. The concept of persistence time, the characteristic time of structural reordering in liquids, is used to compute the solvent's local viscosity. With an increase in the degree of confinement, the confining matrix significantly influences the solvent molecule's local viscosity present in the protein hydration layer through intermolecular interactions. This effect contributes to the enhanced drag force on protein motion, causing a reduction in the rotational diffusion coefficient. Simulation results suggest that the direct matrix-protein non-bonded interaction is responsible for the occasional jump and discontinuity in orientational motion when the protein is in very tight confinement.

Automated summary

The study investigates the anomaly in solvated protein's rotational dynamics under confinement by exploring the viscosity variation of solvent near a solid surface. As the degree of confinement increases, the confining matrix significantly influences the local viscosity of solvent molecules in the protein hydration layer, leading to enhanced drag force on protein motion. The direct matrix-protein non-bonded interaction is found to be responsible for occasional jumps and discontinuities in the protein's orientational motion under tight confinement.