Alpha-RgIA, a novel conotoxin that blocks the alpha9alpha10 nAChR: structure and identification of key receptor-binding residues

J Mol Biol. 2008 Apr 4;377(4):1216-27. doi: 10.1016/j.jmb.2008.01.082. Epub 2008 Feb 4.


Alpha-conotoxins are small disulfide-constrained peptides from cone snails that act as antagonists at specific subtypes of nicotinic acetylcholine receptors (nAChRs). The 13-residue peptide alpha-conotoxin RgIA (alpha-RgIA) is a member of the alpha-4,3 family of alpha-conotoxins and selectively blocks the alpha9alpha10 nAChR subtype, in contrast to another well-characterized member of this family, alpha-conotoxin ImI (alpha-ImI), which is a potent inhibitor of the alpha7 and alpha3beta2 nAChR subtypes. In this study, we have altered side chains in both the four-residue and the three-residue loops of alpha-RgIA, and have modified its C-terminus. The effects of these changes on activity against alpha9alpha10 and alpha7 nAChRs were measured; the solution structures of alpha-RgIA and its Y10W, D5E, and P6V analogues were determined from NMR data; and resonance assignments were made for alpha-RgIA [R9A]. The structures for alpha-RgIA and its three analogues were well defined, except at the chain termini. Comparison of these structures with reported structures of alpha-ImI reveals a common two-loop backbone architecture within the alpha-4,3 family, but with variations in side-chain solvent accessibility and orientation. Asp5, Pro6, and Arg7 in loop 1 are critical for blockade of both the alpha9alpha10 and the alpha7 subtypes. In loop 2, alpha-RgIA [Y10W] had activity near that of wild-type alpha-RgIA, with high potency for alpha9alpha10 and low potency for alpha7, and had a structure similar to that of wild type. By contrast, Arg9 in loop 2 is critical for specific binding to the alpha9alpha10 subtype, probably because it is larger and more solvent accessible than Ala9 in alpha-ImI. Our findings contribute to a better understanding of the molecular basis for antagonism of the alpha9alpha10 nAChR subtype, which is a target for the development of analgesics for the treatment of chronic neuropathic pain.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Conotoxins / chemistry*
  • Conotoxins / metabolism*
  • Conserved Sequence
  • Models, Molecular
  • Molecular Sequence Data
  • Nicotinic Antagonists / chemistry
  • Nicotinic Antagonists / metabolism
  • Protein Subunits / metabolism*
  • Rats
  • Receptors, Nicotinic / metabolism*
  • Sequence Homology, Amino Acid
  • Substrate Specificity


  • Chrna10 protein, rat
  • Conotoxins
  • Nicotinic Antagonists
  • Protein Subunits
  • Receptors, Nicotinic
  • conotoxin alpha-RgIA, Conus regius
  • nAChR alpha9

Associated data

  • PDB/2JUQ
  • PDB/2JUR
  • PDB/2JUS
  • PDB/2JUT