Solution Structure of the Potassium Channel Inhibitor Agitoxin 2: Caliper for Probing Channel Geometry

Protein Sci. 1995 Aug;4(8):1478-89. doi: 10.1002/pro.5560040805.

Abstract

The structure of the potassium channel blocker agitoxin 2 was solved by solution NMR methods. The structure consists of a triple-stranded antiparallel beta-sheet and a single helix covering one face of the beta-sheet. The cysteine side chains connecting the beta-sheet and the helix form the core of the molecule. One edge of the beta-sheet and the adjacent face of the helix form the interface with the Shaker K+ channel. The fold of agitoxin is homologous to the previously determined folds of scorpion venom toxins. However, agitoxin 2 differs significantly from the other channel blockers in the specificity of its interactions. This study was thus focused on a precise characterization of the surface residues at the face of the protein interacting with the Shaker K+ channel. The rigid toxin molecule can be used to estimate dimensions of the potassium channel. Surface-exposed residues, Arg24, Lys27, and Arg31 of the beta-sheet, have been identified from mutagenesis studies as functionally important for blocking the Shaker K+ channel. The sequential and spatial locations of Arg24 and Arg31 are not conserved among the homologous toxins. Knowledge on the details of the channel-binding sites of agitoxin 2 formed a basis for site-directed mutagenesis studies of the toxin and the K+ channel sequences. Observed interactions between mutated toxin and channel are being used to elucidate the channel structure and mechanisms of channel-toxin interactions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Cloning, Molecular
  • Hydrogen Bonding
  • Magnetic Resonance Spectroscopy
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Potassium Channel Blockers*
  • Potassium Channels*
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Scorpion Venoms / chemistry*
  • Scorpion Venoms / genetics
  • Scorpion Venoms / pharmacology
  • Sequence Homology, Amino Acid
  • Shaker Superfamily of Potassium Channels
  • Solutions

Substances

  • Potassium Channel Blockers
  • Potassium Channels
  • Scorpion Venoms
  • Shaker Superfamily of Potassium Channels
  • Solutions
  • agitoxin 2