mu-Conotoxin PIIIA, a new peptide for discriminating among tetrodotoxin-sensitive Na channel subtypes.
We report the characterization of a new sodium channel blocker, mu-conotoxin PIIIA(mu-PIIIA). The peptide has been synthesized chemically and its disulfide bridging pattern determined. The structure of the new peptide is: [sequence: see text] where Z = pyroglutamate and O = 4-trans-hydroxyproline. We demonstrate that Arginine-14 (Arg14) is a key residue; substitution by alanine significantly decreases affinity and results in a toxin unable to block channel conductance completely. Thus, like all toxins that block at Site I, mu-PIIIA has a critical guanidinium group. This peptide is of exceptional interest because, unlike the previously characterized mu-conotoxin GIIIA (mu-GIIIA), it irreversibly blocks amphibian muscle Na channels, providing a useful tool for synaptic electrophysiology. Furthermore, the discovery of mu-PIIIA permits the resolution of tetrodotoxin-sensitive sodium channels into three categories: (1) sensitive to mu-PIIIA and mu-conotoxin GIIIA, (2) sensitive to mu-PIIIA but not to mu-GIIIA, and (3) resistant to mu-PIIIA and mu-GIIIA (examples in each category are skeletal muscle, rat brain Type II, and many mammalian CNS subtypes, respectively). Thus, mu-conotoxin PIIIA provides a key for further discriminating pharmacologically among different sodium channel subtypes.
Shon
K J
KJ
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106, USA.
Olivera
B M
BM
Watkins
M
M
Jacobsen
R B
RB
Gray
W R
WR
Floresca
C Z
CZ
Cruz
L J
LJ
Hillyard
D R
DR
Brink
A
A
Terlau
H
H
Yoshikami
D
D
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D055598:Chemical Phenomena; D002621:Chemistry; D020916:Conotoxins; D018076:DNA, Complementary / Q000235:genetics; D004557:Electric Organ / Q000378:metabolism; D004558:Electric Stimulation; D004593:Electrophorus / Q000378:metabolism; D007536:Isomerism; D008969:Molecular Sequence Data; D008974:Mollusca / Q000235:genetics; D009132:Muscles / Q000187:drug effects / Q000502:physiology; D009154:Mutation / Q000235:genetics; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D011894:Rana pipiens; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology; D013329:Structure-Activity Relationship; D013779:Tetrodotoxin / Q000494:pharmacology*
D020916:Conotoxins; D018076:DNA, Complementary; D010456:Peptides, Cyclic; D015222:Sodium Channels; C112845:mu-conotoxin PIIIA; D012530:Saxitoxin; D013779:Tetrodotoxin