title: Determination of the three-dimensional structure of margatoxin by 1H, 13C, 15N triple-resonance nuclear magnetic resonance spectroscopy.
abstract: The solution structure of the 39-residue peptide margatoxin, a scorpion toxin that selectively blocks the voltage-gated potassium-channel Kv1.3, has been determined by NMR spectroscopy. The toxin was isotopically labeled with 13C and 15N and studied using two-dimensional homonuclear and three- and four-dimensional heteronuclear NMR spectroscopy. The final structure was determined using 501 constraints, comprising 422 NOE constraints, 60 dihedral angle constraints, 9 disulfide constraints, and 10 hydrogen bond constraints. Structures were initially determined with the program PEGASUS and subsequently refined with X-PLOR. The average rms deviation from a calculated average structure for the backbone atoms of residues 3-38 is 0.40 A. A helix is present from residues 11 to 20 and includes two proline residues at positions 15 and 16. A loop at residues 21-24 leads into a two-strand antiparallel sheet from residues 25 to 38 with a turn at residues 30-33. Residues 3-6 run adjacent to the 33-38 strand but do not form a canonical beta-strand. The two additional residues of margatoxin, relative to the related toxins charybdotoxin and iberiotoxin, insert in a manner that extends the beta-sheet by one residue. Otherwise, the global structure is very similar to that of these two other toxins. The longer sheet may have implications for channel selectivity.
authors.affiliation: Department of Biophysical Chemistry, Merck Research Laboratories, Rahway, New Jersey 07065.
authors.forename: B A
authors.initials: BA
authors.lastname: Johnson
authors.forename: S P
authors.initials: SP
authors.lastname: Stevens
authors.forename: J M
authors.initials: JM
authors.lastname: Williamson
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004220:Disulfides / Q000737:chemistry; D004926:Escherichia coli; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009498:Neurotoxins / Q000737:chemistry* / Q000235:genetics; D016133:Polymerase Chain Reaction; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D012604:Scorpion Venoms; D016415:Sequence Alignment; D012984:Software
chemical_list: D004220:Disulfides; D009498:Neurotoxins; D011994:Recombinant Proteins; D012604:Scorpion Venoms; C077910:margatoxin