Solution Structure of δ-Am2766: A Highly Hydrophobic δ-Conotoxin from Conus amadis That Inhibits Inactivation of Neuronal Voltage-Gated Sodium Channels

Authors

  • Siddhartha P. Sarma,

    1. Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India (phone: +91 (80) 2293 2839; fax: +91 (80) 2360 0535)
    Search for more papers by this author
  • G. Senthil Kumar,

    1. Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India (phone: +91 (80) 2293 2839; fax: +91 (80) 2360 0535)
    Search for more papers by this author
  • S. Sudarslal,

    1. Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India (phone: +91 (80) 2293 2839; fax: +91 (80) 2360 0535)
    Search for more papers by this author
  • Prathima Iengar,

    1. Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India (phone: +91 (80) 2293 2839; fax: +91 (80) 2360 0535)
    Search for more papers by this author
  • P. Ramasamy,

    1. Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India (phone: +91 (80) 2293 2839; fax: +91 (80) 2360 0535)
    Search for more papers by this author
  • Sujit K. Sikdar,

    1. Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India (phone: +91 (80) 2293 2839; fax: +91 (80) 2360 0535)
    Search for more papers by this author
  • K. S. Krishnan,

    1. Tata Institute of Fundamental Research, Mumbai, Maharashtra-400005, India
    2. National Center for Biological Science, UAS-GKVK Campus, Bangalore, Karnataka-560065, India
    Search for more papers by this author
  • Padmanabhan Balaram

    1. Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka-560012, India (phone: +91 (80) 2293 2839; fax: +91 (80) 2360 0535)
    Search for more papers by this author

Abstract

The three-dimensional (3D) NMR solution structure (MeOH) of the highly hydrophobic δ-conotoxin δ-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, Cα, C) and (all) heavy atoms were 0.62±0.20 and 1.12±0.23 Å, 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 δ-Am2766 consists of a triple-stranded antiparallel β-sheet, and of four turns. The three disulfides form the classical ‘inhibitory cysteine knot’ motif. So far, only one tertiary structure of a δ-conotoxin has been reported; thus, the tertiary structure of δ-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 δ-Am2766. Unlike δ-Am2766, Am2735 does not inhibit the fast inactivation of Na+ currents in rat brain Nav1.2 Na+ channels at concentrations up to 200 nM.

Ancillary