Paramagnetic effects in structural determination, interactions and dynamics of proteins in vitro and in cells

Abstract

Paramagnetic effects are valuable structural restraints in study of structures, dynamics and interactions of proteins by means of NMR spectroscopy. Site-specific tagging of proteins with paramagnetic ions is generally required to achieve these paramagnetic effects. In this review, we first introduce the concept of paramagnetic effects including paramagnetic relaxation enhancement (PRE), pseudocontact shift (PCS) and residual dipolar couplings (RDCs), which are generally used in biomolecular NMR. Thereafter, strategies of site-specific paramagnetic tagging of proteins are outlined, and the paramagnetic effects are evaluated. On the basis of paramagnetic tagging methods described above, the applications of paramagnetic NMR in characterization of multi-domain protein replacement, 3D structural determination of unstable and low-abundance enzyme intermediate complex in real time condition, and 3D structural determination of proteins in live cells using PCSs are introduced. NMR optimized paramagnetic tags suitable for achieving high spatial resolution of distances determined by double electron-electron resonance (DEER) are reviewed. In the end, the applications of DEER measurement in characterization of protein structures in cells are demonstrated. Paramagnetic NMR and electron paramagnetic resonance (EPR) in characterization of proteins in cells is shown as a powerful technique in structural biology and chemical biology, and the development of biological compatible methods of protein modifications suitable for NMR and EPR applications are in high demand. In summary, paramagnetic tagging proteins are a powerful tool in elucidation of protein structures, dynamics and interactions in chemical and structural biology and it is surely to find wide applications in cells.