Proteins' Dynamics, Hydration and Conformational Changes Studied by EPR

Abstract

Site-directed spin labeling EPR enables detection of conformational changes in proteins with almost no restriction in the environmental conditions. Key information for structural analysis is provided by changes in the dynamics of spin-labeled sites and by interspin distances between selected pairs of labels. Dynamics are detected by continuous wave EPR, interspin distances by pulse dipolar techniques (DEER or PELDOR being the most common). The long-range EPR distance constraints, combined with existing structural data at atomic level for one state of the protein, enable the creation of coarse-grained models of complex protein rearrangements in their physiological milieu. Each protein conformational transition due to oligomerization, ligand binding, transfer from a water to a membrane environment, etc. is also tightly coupled to rearrangements in the hydration water surrounding the different protein interfaces. Changes in local hydration dynamics and water accessibility can be monitored directly and with high precision at physiological temperature using Overhauser dynamic nuclear polarization (ODNP), which has several advantages with respect to other EPR techniques which provide water accessibility data. We will show examples of structural studies in which the changes in the protein and its surrounding water environment are observed. Examples will be given on ABC transporters, Bcl-2 proteins, and light receptors.