RESUMO
Crystal and cryo-EM structures of the glucagon-like peptide-1 receptor (GLP-1R) and glucagon receptor (GCGR) bound with their peptide ligands have been obtained with full-length constructs, indicating that the extracellular domain (ECD) is indispensable for specific ligand binding. This article complements these data with studies of ligand recognition of the two receptors in solution. Paramagnetic NMR relaxation enhancement measurements using dual labeling with fluorine-19 probes on the receptor and nitroxide spin labels on the peptide ligands provided new insights. The glucagon-like peptide-1 (GLP-1) was found to interact with GLP-1R by selective binding to the extracellular surface. The ligand selectivity toward the extracellular surface of the receptor was preserved in the transmembrane domain (TMD) devoid of the ECD. The dual labeling approach further provided evidence of cross-reactivity of GLP-1R and GCGR with glucagon and GLP-1, respectively, which is of interest in the context of medical treatments using combinations of the two polypeptides.
RESUMO
Disulfide-containing detergents (DCDs) are introduced, which contain a disulfide bond in the hydrophobic tail. DCDs form smaller micelles than corresponding detergents with linear hydrocarbon chains, while providing good solubilization and reconstitution of membrane proteins. The use of this new class of detergents in structural biology is illustrated with solution NMR spectra of the human G protein-coupled receptor A2A AR, which is an α-helical protein, and the ß-barrel protein OmpX from E. coli.