The CGRPmut and AM peptides adopted receptor-bound conformations different from typical α-helical class B GPCR peptide ligands. CGRPmut and AM are characterized by a shared turn structure that positions their C-terminal residue to occupy the pocket near the RAMP. Previous studies indicated the presence of turns in the C-terminal region of CGRP (and an absence of α-helix in this area), but how this region interacted with the receptor was unclear (Carpenter et al., 2001; Watkins et al., 2013b). Prior to the turns, the peptides diverge in their structure and interactions with CLR, but they contact the same area of CLR with little or no peptide secondary structure. NMR structures of CGRP and AM suggested that α-helix is restricted to residues 8-18/22-34 of these peptides (Boulanger et al., 1995; Breeze et al., 1991; Pérez-Castells et al., 2012; Watkins et al., 2013a) and indeed the C-terminal regions of both contain helix-breaking Pro residues (Figure 1D). Accordingly, the lack of substantial helical content in the bound peptide fragments is consistent with what is known about the structures of the full-length peptides. A turn structure and paucity of α-helicity may be a general feature of the receptor ECD-binding portions of CT family peptides.