Dynamic Studies Of Sweet Family Sugar Transporters Through Nmr Spectroscopy

Sugar is a primary carbon source for prokaryotes, plants, and humans. Recently, a new family of sugar transporters called SWEETs was discovered and found to transport a variety of mono- and disaccharides across the cell membrane. These proteins exist in all eukaryotic kingdoms including plants, fungi, and animals. SWEETs have ubiquitous expression throughout human cell lines and have been proposed to help mediate vesicular glucose efflux from intestine and liver cells. Mutations in sugar transporters lead to a variety of diseases related to homeostatic imbalance of sugars. Therefore, elucidating the sugar transport mechanism of this family of proteins is essential for developing therapeutic drugs for treatment of diseases related to the homeostatic imbalance of sugars. To date, the transport mechanism has been challenging to study due to the relatively weak binding affinity and difficulties associated with capturing a substrate bound structure of SWEET transporters. To provide atomic scale insight under functional conditions, a combination of solid-state and solution nuclear magnetic resonance (NMR) spectroscopy was used to probe conformational dynamics of this family of transporters upon substrate binding. Solid-state NMR experiments in native E. coli lipid bilayers were utilized to study the interactions between sugar substrates and the binding pocket of SWEETs. In addition, solution NMR in native-like lipid nanodiscs were used for analyzing conformational dynamics in this family of membrane proteins. The site-specific resolution available from NMR provided insights into protein dynamics, the nature of protein-substrate specificity, and the transport mechanism of the SWEET family.