Abstract: Protein isotope labeling is crucial for NMR studies of the three-dimensional structure and dynamics of proteins in solution. Protein expression systems and isotope labeling have been widely used, both of which have been proven useful. However, as the field progresses, the studies on protein with NMR are becoming increasingly difficult with these conventional techniques. Recently, some new isotope protein labeling strategies and new protein expression systems have emerged as tools for studying large proteins by solution NMR. In this paper, these novel protein isotope labeling methods and alternative protein expression systems are reviewed.

Key words: NMR, isotope labeling, protein expression systems, 3D solution structures of proteins