Solution structure and functional characterization of SGTx1, a modifier of Kv2.1 channel gating.
SGTx1 is a peptide toxin isolated from the venom of the spider Scodra griseipes that has been shown to inhibit outward K(+) currents in rat cerebellar granule neurons. Although its amino acid sequence is known to be highly (76%) homologous with that of hanatoxin (HaTx), a well-characterized modifier of Kv2.1 channel gating, the structural and functional characteristics of SGTx1 remain largely unknown. Here we describe the NMR solution structure of SGTx1, the mechanism of its interaction with Kv2.1 channels, and its effect on channel activity once bound. The NMR structure of SGTx1 contains a molecular fold closely resembling the "inhibitor cystine knot" of HaTx, which is composed of an antiparallel beta-sheet and four chain reversals stabilized by three disulfide bonds. Functionally, SGTx1 reversibly inhibited K(+) currents in oocytes expressing Kv2.1 channels. Moreover, generation of steady-state activation curves showed that, consistent with other gating modifiers, SGTx1 acted by shifting the activation of the channel to more depolarized voltages. Thus, the surface profile and mechanism of action of SGTx1 are similar to those of HaTx. Still, detailed comparison of SGTx1 with HaTx revealed differences in binding affinity and conformational homogeneity that result from differences in the charge distribution at the binding surface and in the amino acid composition of the respective beta-hairpin structures in the peptides.
Lee
Chul Won
CW
Department of Life Science, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea.
Kim
Sunghwan
S
Roh
Soung Hun
SH
Endoh
Hiroshi
H
Kodera
Yoshio
Y
Maeda
Tadakazu
T
Kohno
Toshiyuki
T
Wang
Julia M
JM
Swartz
Kenton J
KJ
Kim
Jae Il
JI
D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D051668:Delayed Rectifier Potassium Channels; D004220:Disulfides / Q000737:chemistry; D015640:Ion Channel Gating / Q000187:drug effects; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009865:Oocytes / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D051669:Shab Potassium Channels; D012996:Solutions; D013111:Spider Venoms / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D040681:Structural Homology, Protein; D013329:Structure-Activity Relationship; D013499:Surface Properties; D014981:Xenopus
D051668:Delayed Rectifier Potassium Channels; D004220:Disulfides; C496991:Kcnb1 protein, rat; D010455:Peptides; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C400227:SGTx1 toxin; D051669:Shab Potassium Channels; D012996:Solutions; D013111:Spider Venoms; C096469:hanatoxin