Ion influence on surface water dynamics and proton exchange at protein surfaces - A unified model for transverse and longitudinal NMR relaxation dispersion

In all biologically relevant media, proteins interact in the presence of surrounding ions, and such inter-actions are water-mediated. Water molecules play a crucial role in the restructuring of proteins in solu-tion and indeed in their biological activity. Surface water dynamics and proton exchange at protein surfaces is investigated here using NMR relaxometry, for two well-known globular proteins, lysozyme and bovine serum albumin, with particular attention to the role of surface ions. We present a unified model of surface water dynamics and proton exchange, accounting simultaneously for the observed lon-gitudinal and transverse relaxation rates. The most notable effect of salt (0.1 M) concerns the slow surface water dynamics, related to rare water molecules embedded in energy wells on the protein surface. This response is protein-specific. On the other hand, the proton exchange time between labile protein-protons and water-protons at the protein surface seems to be very similar for the two proteins and is insensitive to the addition of salts at the concentration studied. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the surface water dynamics and proton exchange at protein surfaces using NMR relaxometry. The addition of salt significantly affects the surface water dynamics, while the proton exchange between labile protein-protons and water-protons remains unchanged.