Interaction of a toxin from the scorpion Tityus serrulatus with a cloned K+ channel from squid (sqKv1A).
A toxin from the scorpion Tityus serrulatus (TsTX-Kalpha) blocks native squid K(+) channels and their cloned counterpart, sqKv1A, at pH 8 ((native)K(d) approximately 20 nM; (sqKv1A)K(d) approximately 10 nM). In both cases, decreasing the pH below 7.0 significantly diminishes the TsTX-Kalpha effect (pK = 6.6). In the cloned squid channel, the pH dependence of the block is abolished by a single point mutation (H351G), and no change in toxin affinity was observed at higher pH values (pH > or =8.0). To further investigate the TsTX-Kalpha-sqKv1A interaction, the three-dimensional structure of TsTX-Kalpha was determined in solution by NMR spectroscopy, and a model of the TsTX-Kalpha-sqKv1A complex was generated. As found for other alpha-K toxins such as charybdotoxin (CTX), site-directed mutagenesis at toxin residue K27 (K27A, K27R, and K27E) significantly reduced the toxin's affinity for sqKv1A channels. This is consistent with the TsTX-Kalpha-sqKv1A model reported here, which has K27 of the toxin inserted into the ion conduction pathway of the K(+) channel. This toxin-channel model also illustrates a possible mechanism for the pH-dependent block whereby lysine residues from TsTX-Kalpha (K6 and K23) are repelled by protonated H351 on sqKv1A at low pH.
Ellis
K C
KC
Department of Biochemistry, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
Tenenholz
T C
TC
Jerng
H
H
Hayhurst
M
M
Dudlak
C S
CS
Gilly
W F
WF
Blaustein
M P
MP
Weber
D J
DJ
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D049832:Decapodiformes; D051668:Delayed Rectifier Potassium Channels; D017952:Ganglia, Invertebrate / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009498:Neurotoxins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D019906:Nuclear Magnetic Resonance, Biomolecular; D009865:Oocytes; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D012604:Scorpion Venoms / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis
D051668:Delayed Rectifier Potassium Channels; D009498:Neurotoxins; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011994:Recombinant Proteins; D012604:Scorpion Venoms; C003609:tityustoxin