Expanding the utility of NMR restraints with paramagnetic compounds: Background and practical aspects

► Introduction of a lanthanide ion into a protein leads to paramagnetic effects and partial alignment. ► Paramagnetic Relaxation Enhancements (PREs), Residual Dipolar Couplings (RDCs), and Pseudo-Contact Shifts (PCSs), among others, can be measured. ► Amplitude of paramagnetic effects depends on metal ions, protein size, and magnetic field strength. ► All paramagnetic effects and effects resulting from partial alignment are reviewed. ► Practical aspects include overview of tags used and characteristics of metal ions.