Structural determinants of the blockade of N-type calcium channels by a peptide neurotoxin.
Neurotoxins that selectively block Na+, K+ or Ca2+ channels have provided valuable information about the functional diversity of the voltage-gated channel superfamily. For Ca2+ channels, a variety of toxins have been found to block individual channel types. The best-known example is omega-conotoxin-GVIA, a member of a large family of peptide toxins derived from venomous cone snails, which potently and selectively blocks N-type Ca2+ channels, allowing their purification, cellular localization, and the elucidation of their roles in Ca2+ entry, neurotransmitter release and neuronal migration. In contrast to Na+ and K+ channels, little is known about the molecular features that underlie Ca(2+)-channel susceptibility to toxin block; it is also unknown whether block occurs by direct physical occlusion or an action on channel gating. Here we describe structural determinants of N-type Ca2+ channel's interaction with omega-conotoxin-GVIA. When chimaeras combining individual motifs from the N-type channel and from a channel insensitive to omega-conotoxin-GVIA were expressed in Xenopus oocytes, each of the four motifs appeared to contribute to interaction with the toxin. The most dramatic effects on toxin interactions were seen at a single cluster of residues in the large putative extracellular loop between IIIS5 and IIIH5, consistent with a direct pore-blocking mechanism. These results provide a starting point for delineating the architecture of the outer vestibule of the Ca2+ channel.
Ellinor
P T
PT
Department of Molecular and Cellular Physiology, Stanford University Medical Center, California 94305.
Zhang
J F
JF
Horne
W A
WA
Tsien
R W
RW
D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000737:chemistry* / Q000187:drug effects* / Q000235:genetics; D002478:Cells, Cultured; D006801:Humans; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000494:pharmacology*; D016296:Mutagenesis; D009498:Neurotoxins / Q000494:pharmacology*; D009865:Oocytes; D010455:Peptides / Q000494:pharmacology*; D011487:Protein Conformation; D051381:Rats; D011993:Recombinant Fusion Proteins; D014981:Xenopus; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008978:Mollusk Venoms; D009498:Neurotoxins; D010455:Peptides; D011993:Recombinant Fusion Proteins; D020866:omega-Conotoxin GVIA