Superposition of the AM-bound and ligand-free CLR:RAMP2 complexes (Kusano et al., 2012) revealed minor CLR conformational differences involving the N-terminal region of α1 moving toward AM in the AM-bound state presumably due to AM-CLR T37 contacts (Figure 3F). CLR loops 3 and 4 do not move as in the CGRPmut-bound structure and there are no significant side-chain conformational differences at the peptide-binding site. The position of RAMP2 relative to CLR varies in the two structures (Figure 3F), but the ligand-free RAMP2 position is probably constrained by formation of the dimer of heterodimers in which the C-terminal end of RAMP2 α2 occupies the peptide-binding site of CLR from the opposing heterodimer (Figure 3G). Dimerization of the CLR:RAMP2 ECD heterodimer thus occludes the AM-binding site, which suggested that the RAMP2 L106R substitution (at the end of RAMP2 α2) was key to obtaining AM-bound crystals.