Aromatic residues play key roles in many proteins, and are involved in protein-ligand and protein-protein interactions. They also can be found in the hydrophobic core of proteins, where they are crucial for protein stability. For these reasons, studying their dynamics can provide rich information on reaction mechanisms and folding. Although solution-state NMR has been used to study the motions of aromatic residues for decades, these studies have been limited to small proteins, due to inherent physical restrictions. A new approach developed by the IBS NMR group, in collaboration with Japanese and Austrian chemists, makes it possible to gain insights into the movements of aromatic residues even in very large proteins. The approach combines solid-state NMR and specific isotopic labelling of phenylalanines or tyrosines. The study by Gauto et al applied this method to the 468 kDa enzyme TET2 protein and demonstrated, among other things, the rotational kinetics of phenylalanines over a wide temperature range, down to -170°C. Temperature-dependent measurements reveal how the motions of the protein are activated when the temperature is increased, with an interesting appearance of motion at about -70 °C, often call the "glass-transition temperature". Furthermore, the approach allowed to infer "invisible" states with life times of microseconds, which, interestingly cluster around a pore located between subunits. This methodology also allows to obtain distance information between aromatic residues and their environment, which are valuable for determining the three-dimensional structures of proteins.
Aromatic Ring Dynamics, Thermal Activation, and Transient Conformations of a 468 kDa Enzyme by Specific 1H-13C Labeling and Fast Magic-Angle Spinning NMR. Gauto DF, Macek P, Barducci A, Fraga H, Hessel A, Terauchi T, Gajan D, Miyanoiri Y, Boisbouvier J, Lichtenecker R, Kainosho M, Schanda P. Journal of the American Chemical Society; 141(28):11183-11195