Applications of REDOR for Distance Measurements in Biological Solids

Knowledge of structural details at an atomic level is important in understanding the function and molecular properties of biomolecules. In situations where crystallography or solution state NMR methods are not applicable, solid state NMR can provide valuable insight without the limitations imposed by the availability of crystals, solubility or molecular weight. In particular dedicated solid state NMR methods enable the determination of selective internuclear distances at high accuracy. A popular and robust technique is rotational echo double resonance (REDOR), which allows the measurement of distances of heteronuclear spin pairs. This magic angle spinning method uses radiofrequency pulses to prevent the dipole-dipole interaction from being averaged by the sample spinning, leading to a reduction of the NMR signal which depends on the internuclear distance. Biological systems constitute a major area of application of the REDOR experiment, and are the focus of this review. First, the theoretical background, developments and experimental considerations of REDOR are discussed, regarding in particular applications on biological samples. Then, an overview of the use of REDOR in a wide range of biological applications, such as ligand binding sites of enzymes, fibrilar proteins, membrane active peptides, transmembrane helices, biomaterials like the peptidoglycan of bacterial cell walls or nucleic acids, is presented. © 2007 Elsevier Ltd. All rights reserved.