Solid-state NMR studies of proteins in condensed phases

Some proteins perform their biological functions by changing their material states through liquid-liquid phase separation. Upon phase separation, the protein condenses into a concentrated liquid phase and sometimes into a gel phase, changing its dynamic properties and intermolecular interactions, thereby regulating cellular functions. Although the biological significance of this phenomenon has been widely recognized by researchers, there is still a lack of a comprehensive understanding of the structural and dynamic properties of the protein in the condensed phase. In this phase, molecules usually contain domains with varied dynamic properties and undergo intermediate exchanges. Magic angle spinning (MAS) solid-state NMR (SSNMR) experiments are very powerful in studying rigid protein polymers such as amyloid. The incorporation of solution-like experiments into SSNMR and the development of J-coupling based MAS SSNMR techniques extend its ability to study partially mobile segments of proteins in a condensed liquid or gel phase which are not visible by solution NMR or dipolar-coupling based SSNMR. Therefore, it has been applied in studying protein condensation and has provided very important information that is hard to obtain by other techniques.