Abstract
Charybdotoxin (CTX) is a peptide of known structure that inhibits Shaker K + channels by a pore-blocking mechanism. Point mutagenesis of all 30 solvent-exposed residues identified the part of the CTX molecular surface making contact with the receptor in the K + channel. All close-contact residues are clustered in a well-defined interaction surface; the shape of this surface implies that the outer opening of the Shaker channel conduction pore abruptly widens to a 25 × 35 Å plateau. A mutagenic scan of the S5–S6 linker sequence of the Shaker K + channel identified those channel residues influencing CTX binding affinity. The Shaker residues making the strongest contribution to toxin binding are located close to the pore-lining sequence, and more distant residues on both sides of this region influence CTX binding weakly, probably by an electrostatic mechanism. Complementary mutagenesis of both CTX and Shaker suggests that Shaker-F425 contacts a specific area near T8 and T9 on the CTX molecular surface. This contact point constrains Shaker-F425 to be located at a 20 Å radial distance from the pore axis and 10–15 Å above the “floor” of the CTX receptor.
Highlights
Charybdotoxin (CTX) belongs to a family of scorpion venom peptides that inhibit voltage-gated and Ca2+. activated K+ channels (Miller et al, 1985; Gimenez Gallego et al, 1988; Crest et al, 1992; Possani et al, 1982; Candia et al, 1992; Garcia-Calvo et al, 1993)
The simplicity of the blocking mechanism has allowed these peptides to be used as molecular probes of K+ channels, pointing to the region of the protein bearing both the CTX receptor and the ion conduction pathway (MacKinnon and Miller,1989; MacKinnon and Yellen, 1990) and demonstrating the tetrameric stoichiometry of the channel complex (MacKinnon, 1991; MacKinnon et al, 1993)
The results demonstrate that CTX presents to the Shaker K+ channel an interaction surface similar to that deduced for the BK channel
Summary
Charybdotoxin (CTX) belongs to a family of scorpion venom peptides that inhibit voltage-gated and Ca2+. activated K+ channels (Miller et al, 1985; Gimenez Gallego et al, 1988; Crest et al, 1992; Possani et al, 1982; Candia et al, 1992; Garcia-Calvo et al, 1993). The peptide's entire internal volume is filled by these 6 cysteine residues, whereas all non-cysteine side chains lie on the surface and project into solvent These molecular characteristics make CTX well suited for analysis of the roles of individual residues in the toxin-receptor interaction, since they favor the likelihood that point mutants will exert only local effects on toxin binding. This locality of point mutations underlies the utility of CTX as a structural probe of the channel (MacKinnon and Miller, 1989; Park and Miller, 1992a, 1992b; Stampe et al, 1994)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
