title: The NMR solution structure of the NMDA receptor antagonist, conantokin-T, in the absence of divalent metal ions.
abstract: The solution conformation of conantokin-T, a Gla-containing 21-residue peptide, (G1 EgammagammaY5QKMLgamma10NLRgammaA15EVKKN20A-amide), in the absence of divalent metal ions, was studied by use of two-dimensional proton NMR spectroscopy. The peptide is helical from the N-terminus to the C-terminus, as defined by upfield-shifted alpha-proton resonances and by characteristic NOE connectivities. Extensive interactions among the amino acid side-chains were identified from the NOESY spectra of this peptide in a buffered aqueous solution. Four hydrophobic residues Tyr5, Met8, Leu9, and Leu12 contact one another in a stable cluster, even in the presence of 6 M urea. The solution structure of conantokin-T is a well-defined alpha-helix, having RMSD values for the backbone and all heavy atoms of 0.40 A and 0.77 A, respectively. Potential repulsion between the negatively-charged side chains of Gla10 and Gla14 is minimized by a Gln6-Gla10 hydrogen bond and by an Arg13-Gla14 ion-pair interaction. The C-terminal amide and the Asn20 side-chain amide both interact with the backbone and minimize fraying at the C-terminal end of the alpha-helix. This study provides a basis to evaluate the changes in peptide conformation concomitant upon the binding of divalent metal ions. In addition, this investigation demonstrates that apo-conantokin-T has almost all of the favorable interactions that are known to contribute to helical stabilization in proteins and monomeric helices.
authors.affiliation: Department of Chemistry and Biochemistry and the Center for Transgene Research, University of Notre Dame, IN 46556, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Warder
authors.forename: Z
authors.initials: Z
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Zhu
authors.forename: M
authors.initials: M
authors.lastname: Prorok
authors.forename: F J
authors.initials: FJ
authors.lastname: Castellino
authors.forename: F
authors.initials: F
authors.lastname: Ni
mesh_terms: D000595:Amino Acid Sequence; D002413:Cations, Divalent; D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists / Q000737:chemistry*; D036341:Intercellular Signaling Peptides and Proteins; D009682:Magnetic Resonance Spectroscopy; D008670:Metals; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*; D012996:Solutions
chemical_list: D002413:Cations, Divalent; D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists; D036341:Intercellular Signaling Peptides and Proteins; D008670:Metals; D008978:Mollusk Venoms; D010455:Peptides; D016194:Receptors, N-Methyl-D-Aspartate; D012996:Solutions; C063571:conantokin-T