Trimethylsilyl reporter groups for NMR studies of conformational changes in G protein-coupled receptors

Large membrane proteins such as G protein-coupled receptors (GPCRs) are difficult for NMR study due to severe signal overlaps and unfavorable relaxation properties. We used a trimethylsilyl (TMS) group as a reporter group for ¹ H NMR study of conformational changes in proteins, utilizing high-intensity ¹ H NMR signals near 0 p.p.m. The β₂ -adrenergic receptor was labeled with TMS groups at two cysteines located at the cytoplasmic ends of helices VI and VII. Binding of various ligands led to changes in ¹ H NMR signals, which manifested that helix VI is sensitive to G protein-specific activation, whereas helix VII is sensitive to β-arrestin-specific activation. Thus, the TMS group is a useful reporter group in NMR for studying conformational changes in membrane proteins such as GPCRs.