title: Solution structure of delta-Am2766: a highly hydrophobic delta-conotoxin from Conus amadis that inhibits inactivation of neuronal voltage-gated sodium channels.
abstract: The three-dimensional (3D) NMR solution structure (MeOH) of the highly hydrophobic delta-conotoxin delta-Am2766 from the molluscivorous snail Conus amadis has been determined. Fifteen converged structures were obtained on the basis of 262 distance constraints, 25 torsion-angle constraints, and ten constraints based on disulfide linkages and H-bonds. The root-mean-square deviations (rmsd) about the averaged coordinates of the backbone (N, C(alpha), C) and (all) heavy atoms were 0.62+/-0.20 and 1.12+/-0.23 A, respectively. The structures determined are of good stereochemical quality, as evidenced by the high percentage (100%) of backbone dihedral angles that occupy favorable and additionally allowed regions of the Ramachandran map. The structure of delta-Am2766 consists of a triple-stranded antiparallel beta-sheet, and of four turns. The three disulfides form the classical 'inhibitory cysteine knot' motif. So far, only one tertiary structure of a delta-conotoxin has been reported; thus, the tertiary structure of delta-Am2766 is the second such example. Another Conus peptide, Am2735 from C. amadis, has also been purified and sequenced. Am2735 shares 96% sequence identity with delta-Am2766. Unlike delta-Am2766, Am2735 does not inhibit the fast inactivation of Na+ currents in rat brain Na(v)1.2 Na+ channels at concentrations up to 200 nM.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India. sidd@mbu.iisc.ernet.in
authors.forename: Siddhartha P
authors.initials: SP
authors.lastname: Sarma
authors.forename: G Senthil
authors.initials: GS
authors.lastname: Kumar
authors.forename: S
authors.initials: S
authors.lastname: Sudarslal
authors.forename: Prathima
authors.initials: P
authors.lastname: Iengar
authors.forename: P
authors.initials: P
authors.lastname: Ramasamy
authors.forename: Sujit K
authors.initials: SK
authors.lastname: Sikdar
authors.forename: K S
authors.initials: KS
authors.lastname: Krishnan
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020916:Conotoxins / Q000737:chemistry* / Q000494:pharmacology*; D052078:Conus Snail / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D015222:Sodium Channels / Q000378:metabolism*
chemical_list: D020916:Conotoxins; D015222:Sodium Channels