Selective peptide antagonist of the class E calcium channel from the venom of the tarantula Hysterocrates gigas.
We describe the first potent and selective blocker of the class E Ca2+channel. SNX-482, a novel 41 amino acid peptide present in the venom of the African tarantula, Hysterocrates gigas, was identified through its ability to inhibit human class E Ca2+ channels stably expressed in a mammalian cell line. An IC50 of 15-30 nM was obtained for block of the class E Ca2+ channel, using either patch clamp electrophysiology or K+-evoked Ca2+ flux. At low nanomolar concentrations, SNX-482 also blocked a native resistant or R-type Ca2+ current in rat neurohypophyseal nerve terminals, but concentrations of 200-500 nM had no effect on R-type Ca2+ currents in several types of rat central neurons. The peptide has the sequence GVDKAGCRYMFGGCSVNDDCCPRLGCHSLFSYCAWDLTFSD-OH and is homologous to the spider peptides grammatoxin S1A and hanatoxin, both peptides with very different ion channel blocking selectivities. No effect of SNX-482 was observed on the following ion channel activities: Na+ or K+ currents in several cultured cell types (up to 500 nM); K+ current through cloned potassium channels Kv1.1 and Kv1. 4 expressed in Xenopus oocytes (up to 140 nM); Ca2+ flux through L- and T-type Ca2+ channels in an anterior pituitary cell line (GH3, up to 500 nM); and Ba2+ current through class A Ca2+ channels expressed in Xenopus oocytes (up to 280 nM). A weak effect was noted on Ca2+ current through cloned and stably expressed class B Ca2+ channels (IC50 > 500 nM). The unique selectivity of SNX-482 suggests its usefulness in studying the diversity, function, and pharmacology of class E and/or R-type Ca2+ channels.
Newcomb
R
R
Elan Pharmaceuticals Inc., Menlo Park, California 94025, USA.
Szoke
B
B
Palma
A
A
Wang
G
G
Chen
X h
Xh
Hopkins
W
W
Cong
R
R
Miller
J
J
Urge
L
L
Tarczy-Hornoch
K
K
Loo
J A
JA
Dooley
D J
DJ
Nadasdi
L
L
Tsien
R W
RW
Lemos
J
J
Miljanich
G
G
D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D002460:Cell Line; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000737:chemistry* / Q000302:isolation & purification / Q000502:physiology; D026902:Potassium Channel Blockers; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers; D013111:Spider Venoms / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D014981:Xenopus
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010455:Peptides; D026902:Potassium Channel Blockers; C115521:SNX 482; D026941:Sodium Channel Blockers; D013111:Spider Venoms