Conformational ensembles of neuromedin C reveal a progressive coil-helix transition within a binding-induced folding mechanism

Neuromedin C (NMC) is a peptide that regulates various processes in the central nervous system and gastrointestinal tract through its interaction with the bombesin receptor subtype-2 (BB2R). Hence, BB2R antagonists hold potential to treat disorders that occur as a result of NMC dysfunction or misregulation. However, their efficient design requires a detailed understanding of the structural features of NMC, which hitherto are unknown. Here we describe the conformational ensembles of NMC in aqueous solution, at five different TFE concentrations to decode its folding pathway, and under its SDS micelle bound state that likely resembles the receptortriggered conformation. NMC displays a disordered but well-defined backbone architecture that undergoes a progressive coil-helix transition with increasing TFE concentrations, first at the C-terminus and then at the N-terminus. NMC also adopts a C-terminal α-helical conformation upon binding to SDS micelles. This micelle binding is directed by hydrophobic interactions that concur with the unfavorable deprotonation of His and its further insertion into the micelle. Moreover, NMR relaxation data reveal that the acquisition of the micelle bound α-helical conformation constrains the NMC flexibility more than the confinement itself. This comprehensive study of the structural behavior of NMC provides essential mechanistic information for the development of new therapeutics to treat neurological, cancer-related or eating disorders.