NMR identification of a partial helical conformation for bombesin in solution

Abstract

The conformation of bombesin in trifluoroethanol/water mixtures has been studied using 1H‐NMR spectroscopy. By a combination of two‐dimensional 1H‐NMR techniques and measurement of vicinal NH‐α‐CH spin‐spin coupling constants, the secondary structure of the molecule has been determined. Bombesin adopts a helical structure in the region from Asn‐6 to Met‐14 with the remaining N‐terminal portion existing as a more extended structure. The structure is very similar to that proposed from Fourier‐transform infrared spectroscopic measurements for bombesin inserted into lipid bilayers [D. Erne & R. Schwyzer (1987) Biochemistry 26, 6316–6319]. The absence of a hydrogen bond between the sidechains of Trp‐8 and His‐12 is discussed in terms of the ionization state of His‐12. Stabilisation of the helix results when His‐12 is in the ionized state. Show more