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Both the aqueous and the lipid-induced structure of eledoisin, an undecapeptide of mollusk origin, have been studied by two-dimensional proton nuclear magnetic resonance spectroscopy and distance geometry calculations. Unambiguous nuclear magnetic resonance assignments of protons have been made with the aid of correlation spectroscopy experiments and nuclear Overhauser effect spectroscopy experiments. The distance constraints obtained from the nuclear magnetic resonance data have been utilized in a distance geometry algorithm to generate a family of structures, which have been refined using restrained energy minimization and dynamics. These data show that, while in water and dimethyl sulfoxide, eledoisin prefers to be in an extended chain conformation, whereas in the presence of perdeuterated dodecylphosphocholine micelles, a membrane model system, helical conformation is induced in the central core and C-terminal region (K4-M11) of the peptide. N terminus, though less defined, also displays some degree of order and a possible turn structure. The conformation adopted by eledoisin in the presence of dodecylphosphocholine micelles is similar to the structural motif typical of neurokinin-2 selective agonists and with that reported for kassinin in hydrophobic environment.

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In an attempt to answer the question of whether or not the so-called tachykinin-like region of the Alzheimer beta-amyloid protein [Abeta(25-35)] can act as a tachykinin, the sequences Abeta(25-35), Abeta(25-35)amide and their norleucine-35 and phenylalanine-31 analogues were synthesized. These peptides were examined with ligand binding studies, electron microscopy, CD and NMR. In all cases some differences were found between the Abeta(25-35) analogue and the corresponding Phe31 peptide. In addition, in ligand displacement studies on tachykinin NK1 receptors, only the Phe31 analogue showed activity comparable to that of genuine tachykinins. We conclude that peptides based on Abeta(25-35) but with a Phe residue at position 31 do display properties typical of a tachykinin, but that peptides with Ile at this position do not.

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The nonmammalian tachykinin eledoisin was investigated by use of CD and two-dimensional NMR techniques. In aqueous solution the peptide is conformationally averaged, but on addition of 50% trifluoroethanol (TFE) or sodium dodecyl sulfate (SDS) it adopts an alpha-helical structure. In TFE/H2O and SDS, residues 6-10 of eledoisin show more conformational order than the terminal regions, which undergo dynamic fraying. A possible turn in the N-terminal "address" region, the putative receptor recognition site of the peptide, is detected by NMR spectroscopy but appears to undergo substantial conformational averaging. The NMR data indicate that the helical central core of eledoisin is better defined in the micellar environment than in TFE; however, partial unfolding via 3(10) intermediates occurs in both cases. The conformational preference for SDS-bound eledoisin was examined by three-dimensional structure calculations using NMR-derived distance information in simulated annealing calculations.

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Chemical modification studies of peptide hormones and random peptides have revealed that seryl hydroxyl groups had enhanced reactivity toward acylating reagents when they occurred in the linear triads His-Xaa-Ser or Ser-Xaa-His (Xaa = any amino acid). O-acylation of serine within these triads was achieved by reaction with N-hydroxysuccinimide esters of biotin (NHS-biotin) and succinic anhydride. Seryl residues not occurring in His-Xaa-Ser/Ser-Xaa-His triads showed no reactivity towards NHS-biotin under reaction conditions described. Results of histidine replacement studies and studies of the pH dependence of O-biotinylation indicated that the increased nucleophilicity of the seryl hydroxyl group was due to intramolecular interaction between the seryl and histidyl residues. Our findings provide strong evidence that such triads represent novel consensus motifs in peptides.

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Commercial sources for neuropeptide radioimmunoassays have made this sensitive tool available to clinical investigators for monitoring the potential involvement of neuropeptides in pain modulation. We measured substance P-like immunoreactivity in the plasma, saliva, and pericardial fluid of subjects with and without pain (chronic and acute) to determine if substance P levels are altered. Some recent studies have suggested that substance P in various body fluids may be a correlate of chronic pain. To test this correlation it is important to ensure that the assay is measuring what it was designed to measure. Therefore, the influence of three tachykinins on the analysis of substance P concentrations was assessed with a commercially available radioimmunoassay kit. A small (approximately 2 to 6%), apparently nonspecific elevation in measured substance P was found when alpha-neurokinin, beta-neurokinin, or eledoisin was incubated with substance P and its antibody. Our results also indicate an apparent specific affinity of the substance P antibody for alpha-neurokinin (above 1,000 pg/ml) and beta-neurokinin (above 5,000 pg/ml). Substance P levels in the body fluids we tested ranged from 0.47 to 62.88 pg/mg protein (47.4 to 230.8 pg/ml). Levels of the tested tachykinins have not been determined in body fluids. If alpha-neurokinin or beta-neurokinin is found to be present in high concentrations in these fluids, this commercially available substance P kit may overestimate substance P levels. The concentrations of tachykinins necessary to interfere specifically with the assay are 10- to 100-fold higher than substance P in body fluids.(ABSTRACT TRUNCATED AT 250 WORDS)

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