Neuropeptide K potently stimulates the hydrolysis of phosphatidylinositol in the rat spinal cord

Three-Dimensional Structure of Neuropeptide K Bound to Dodecylphosphocholine Micelles

Neuropeptide K (NPK), an N-terminally extended form of neurokinin A (NKA), represents the most potent and longest lasting vasodepressor and cardiomodulatory tachykinin reported thus far. NPK has been shown to have high selectivity for the NK2 receptor. Because the micelle-associated structure may be relevant to the NPK-receptor interaction, the three-dimensional structure of the NPK in aqueous and micellar environments has been studied by two-dimensional proton nuclear magnetic resonance (2D (1)H NMR spectroscopy) and distance geometry calculations. Proton NMR assignments have been carried out with the aid of correlation spectroscopy (DQF-COSY and TOCSY) and nuclear Overhauser effect spectroscopy (NOESY and ROESY) experiments. The interproton distances and dihedral angle constraints obtained from the NMR data have been used in torsion angle dynamics algorithm for NMR applications (DYANA) to generate a family of structures, which have been refined using restrained energy minimization and dynamics. The results show that in an aqueous environment NPK lacks a definite secondary structure, although some turn-like elements are present in the N terminus. The structure is well-defined in the presence of dodecylphosphocholine micelles. The global fold of NPK bound to DPC micelles consists of two well-defined helices from residues 9 to 18 and residues 27 to 33 connected by a noncanonical beta turn. The N terminus of the peptide is characterized by a 3(10) helix or a series of dynamic beta turns. The conformational range of the peptide revealed by NMR and circular dichroism (CD) studies has been analyzed in terms of characteristic secondary features. The observed conformational features have been further compared to a NKA and neuropeptide gamma (NPgamma) potent endogenous agonist for the NK2 receptor.

Cardiovascular and behavioural effects of centrally administered neuropeptide K in the rat: receptor characterization

1. The cardiovascular and behavioural responses to intracerebroventricularly (i.c.v.) administered neuropeptide K (NPK) were studied in conscious rats. The central effects of NPK were characterized by pretreatment (i.c.v.) with selective antagonists for the NK1 ((+/-)-CP 96345 and RP 67580), NK2 (SR 48968) and NK3 (R 487) receptors. 2. NPK (10-65 pmol) induced tachycardia and dose-dependent increases of mean arterial blood pressure. The cardiovascular responses reached a maximum within 3 min post-injection and lasted for more than 1 h. Concurrently, NPK produced dose-dependent increases of face washing, head scratching, grooming, walking and wet dog shakes. 3. A desensitization of most of the behavioural responses (except head scratching) but not of the cardiovascular response was shown when two consecutive injections of 25 pmol NPK were given 24 h apart. 4. Both the cardiovascular and behavioural responses (except the head scratching) to 25 pmol NPK were blocked by pre-administration (i.c.v.) of 6.5 nmol (+/-)-CP 96345 or RP 67580 given 5 min earlier. No inhibition of NPK responses was observed when 6.5 nmol SR 48968 or R 487 were used in a similar study. Additionally, NPK effects were significantly reduced 24 h after the prior injection of (+/-)-CP 96345 but not of RP 67580. 5. These results support the involvement of NK1 receptors in the cardiovascular and behavioural effects of i.c.v. NPK. Thus, this peptide may play a putative role in central cardiovascular regulation as it is the most potent endogenous tachykinin described centrally, to date.