Solution structure of the potassium channel inhibitor agitoxin 2: caliper for probing channel geometry.
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.
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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Krezel
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Kasibhatla
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Hidalgo
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MacKinnon
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Wagner
D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012604:Scorpion Venoms / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D051637:Shaker Superfamily of Potassium Channels; D012996:Solutions
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D012604:Scorpion Venoms; D051637:Shaker Superfamily of Potassium Channels; D012996:Solutions; C087603:agitoxin 2