Fig. 1. Potential approaches to study GPCRs from fragments. (A) Recognition of extracellular (EC) domains. The EC N-terminal domain is studied in isolation. Alternatively, the EC loops are grafted onto a β-barrel protein (OmpA) to study binding by NPY peptide ligands. (B) Formation of interhelical contacts studied in receptors that have been dissected into 2-TM fragments. (C) NMR is used to study fragments of increasing length to infer interhelical contact formation and stability of the TM helices during biogenesis in a lipid environment.