1H, 13C and 15N resonance assignments of the third intracellular loop of the muscarinic acetylcholine receptor M1.

G protein-coupled receptors (GPCRs) are highly dynamic seven-transmembrane (7TM) proteins that respond to various extracellular stimuli and elicit diverse intracellular signaling cascades. The third intracellular loops (ICL3s) of the GPCRs are intrinsically disordered and play important roles in signaling. The muscarinic acetylcholine receptors (mAChRs) harbor extremely long ICL3s, which comprise over a hundred amino acid residues and contain multiple phosphorylation sites. Due to their intrinsic flexibility, ICL3s are commonly absent or unobservable in cryo-EM or X-ray structures, and there has been a lack of structural and dynamics study of these regions. Herein, we report the ¹H, ¹³C and ¹⁵N chemical shift assignments of the M1 muscarinic receptor ICL3, which provides a basis for further NMR studies of its conformational dynamics, post-translational modifications and interactions.