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Mapping the site of block by tetrodotoxin and saxitoxin of sodium channel II
Author(s) -
Terlau Heinrich,
Heinemann Stefan H.,
Stühmer Walter,
Pusch Michael,
Conti Franco,
Imoto Keiji,
Numa Shosaku
Publication year - 1991
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(91)81159-6
Subject(s) - sodium channel , xenopus , tetrodotoxin , chemistry , biophysics , amino acid , conductance , saxitoxin , sodium , microinjection , complementary dna , biochemistry , microbiology and biotechnology , biology , toxin , gene , physics , organic chemistry , condensed matter physics
The SS2 and adjacent regions of the 4 internal repeats of sodium channel II were subjected to single mutations involving, mainly, charged amino acid residues. These sodium channel mutants, expressed in Xenopus oocytes by microinjection of cDNA‐derived mRNAs, were tested for sensitivity to tetrodotoxin and saxitoxin and for single‐channel conductance. The results obtained show that mutations involving 2 clusters of predominantly negatively charged residues, located at equivalent positions in the SS2 segment of the 4 repeats, strongly reduce toxin sensitivity, whereas mutations of adjacent residues exert much smaller or no effects. This suggests that the 2 clusters of residues, probably forming ring structures, take part in the extracellular mouth and/or the pore wall of the sodium channel. This view is further supported by our finding that all mutations reducing net negative charge in these amino acid clusters cause a marked decrease in single‐channel conductance.