Spatially heterogeneous surface water diffusivity around structured protein surfaces at equilibrium

摘要

Hydration water on the surface of a protein is thought to mediate the thermodynamics of protein-ligand interaction. For hydration water to play a role beyond modulating global protein solubility or stability, the thermodynamic properties of hydration water must reflect on the properties of the heterogeneous protein surface, and thus spatially vary over the protein surface. A potent read-out of local variations in thermodynamic properties of hydration water is its equilibrium dynamics spanning picosecond to nanosecond timescales. In this study, we rely on Overhauser dynamic nuclear polarization (ODNP) to probe the equilibrium hydration water dynamics on the globular protein Chemotaxis Y (CheY), in dilute solution, at select sites located on the protein surface. ODNP reports on site-specific hydration dynamics within 5–10 Å of a label tethered to the biomolecular surface on two separate timescales of motion, corresponding to diffusive water (DW) and protein-water coupled motions referred to as bound water (BW). We find DW dynamics to be highly heterogeneous across the surface of CheY, while also finding significant populations of BW. We identify a significant correlation between DW dynamics and the local hydropathy of the CheY protein surface, as empirically determined by molecular dynamics (MD) simulations, and find the more hydrophobic sites to be hydrated with slower diffusing water. We furthermore compare the DW dynamics and BW population on the surface of CheY to that of another globular protein Annexin XII (Anx), two intrinsically disordered proteins (IDPs) ΔTau-187 and α-synuclein, CheY-inspired 5 residue peptides, polyproline-based peptides with systematic charge variation, and DPPC/DOPC liposomes. The DW dynamics on Anx is similarly heterogeneous as on CheY, and there is significant BW population on both Anx and CheY. In contrast, DW dynamics is relatively homogeneous on IDP and liposome surfaces, while BW is entirely absent. The heterogeneity in hydration water properties suggests that a structured protein surface has the capacity to encode information into its hydration water to mediate the free energy of interactions involving the protein surface.