title: 1H-nuclear magnetic resonance studies of the neuropeptide head activator.
abstract: The 1H-NMR spectrum of the neuropeptide head activator in aqueous solution has been completely assigned by two-dimensional NMR spectroscopy and selective deuteration. The apparent pseudo-first-order exchange rate, kex, of the backbone amide protons and the correspondent activation enthalpies, delta H not equal to, were determined. The exchange rates decrease and the activation enthalpies increase from the N-terminal to the C-terminal part of the peptide. The exchange rates vary from 21 to 0.3 s-1 at 274 K, the activation enthalpies from 60 to 75 kJ.mol-1. The pK values of the terminal carboxyl group and of the lysine amino group have been estimated as 3.3 and 10.3, respectively. The NMR results are in line with a dimeric structure in an antisymmetric arrangement of the subunits, forming an antiparallel beta-pleated sheet between C-terminal segments. The peptide bonds between pGlu-1, Pro-2 and Pro-3 are predominantly in trans-configuration, in fact no cis-isomers can be observed spectroscopically. The structure appears to be very stable; in the temperature and pH range studied, i.e., from 274 to 338 K and from pH 0.8 to pH 11.6, there are no spectroscopic indications for a global structural change.
authors.affiliation: Max-Planck-Institute for Medical Research, Department of Biophysics, Heidelberg, F.R.G.
authors.forename: R
authors.initials: R
authors.lastname: Saffrich
authors.forename: H R
authors.initials: HR
authors.lastname: Kalbitzer
authors.forename: H
authors.initials: H
authors.lastname: Bodenmüller
authors.forename: P
authors.initials: P
authors.lastname: Muhn
authors.forename: R
authors.initials: R
authors.lastname: Pipkorn
authors.forename: H C
authors.initials: HC
authors.lastname: Schaller
mesh_terms: D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D009479:Neuropeptides; D011487:Protein Conformation; D011761:Pyrrolidonecarboxylic Acid / Q000032:analysis / Q000031:analogs & derivatives
chemical_list: D009479:Neuropeptides; C032522:head activator peptide; D011761:Pyrrolidonecarboxylic Acid