Multiple residues specify external tetraethylammonium blockade in voltage-gated potassium channels.
We have mapped residues in the carboxyl half of the P region of a voltage-gated K+ channel that influence external tetraethylammonium (TEA) block. Fifteen amino acids were substituted with cysteine and expressed in oocytes from monomeric or heterodimeric cRNAs. From a total of six mutant channels with altered TEA sensitivity, three were susceptible to modification by extracellularly applied charged methanethiosulfonates (MTSX). Another residue did not affect TEA block but was protected from MTSX by TEA. MTSX modification of position Y380C, thought to form the TEA binding site, affected TEA affinity only moderately, and this effect could be reversed by additional charge transfer from an oppositely charged MTSX analog. The results show that TEA block is modulated from multiple sites, including residues located deep in the pore and that several side chains besides that of Y380 are exposed at the TEA receptor.
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA.
J M
JM
Pascual
C C
CC
Shieh
G E
GE
Kirsch
A M
AM
Brown
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*; D014982:Xenopus laevis
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011994:Recombinant Proteins; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium