Neuropeptide gamma belongs to
tachykinin families which have a common C-terminal amino acid sequence (Phe-X-Leu-Met-NH2) and which induce various
biological responses including salivation,
hypotension, and contraction of gastrointestinal, respiratory, and urinary smooth muscle. In the present study, we present the
solution structures of
neuropeptide gamma (NPgamma) from
gold fish (G-NPgamma) and mammalian NPgamma (M-NPgamma), as determined by nuclear magnetic resonance (NMR) spectroscopy in 50%
trifluoroethanol (
TFE)/water (1 : 1, v/v)
solution and 200 mm
sodium dodecyl sulfate (SDS)
micelles. In aqueous
TFE solution, G-NPgamma has a alpha-helical conformation in the region of His12-Met21 and a short helix in the N-terminal region, and has a beta-turn from Arg9 to Arg11 in between. In aqueous
TFE solution, M-NPgamma also has alpha-helical conformations both in the C-terminal region and the N-terminal region and a beta-turn from His9 to Arg11 in between. In SDS
micelle, the structure of G-NPgamma contains a stable alpha-helix from His12 to Met21 and a beta-turn from Arg9 to Arg11, while M-NPgamma has a short helix from Ser16 to Met21. The region from His12 to Met21 corresponds to the amino acid sequence of
neurokinin A.
Neuropeptide gamma may act as a precursor of
neurokinin A and the post-translational processing of this
peptide involves the enzymatic attack of the basic beta-turn region from residue 9 to residue 11 in the middle. From our relaxation study, it could be suggested that in fish system G-NPgamma induces the
biological actions corresponding to those of
substance P in mammalian system. The structures of G-NPgamma and M-NPgamma contain alpha-helical structures at the C-terminus and this helix seems to promote the affinity for NK1 and/or NK2 receptor.