Solution structure of GxTX-1E, a high-affinity tarantula toxin interacting with voltage sensors in Kv2.1 potassium channels .
GxTX-1E is a neurotoxin recently isolated from Plesiophrictus guangxiensis venom that inhibits the Kv2.1 channel in pancreatic beta-cells. The sequence of the toxin is related to those of previously studied tarantula toxins that interact with the voltage sensors in Kv channels, and GxTX-1E interacts with the Kv2.1 channel with unusually high affinity, making it particularly useful for structural and mechanistic studies. Here we determined the three-dimensional solution structure of GxTX-1E using NMR spectroscopy and compared it to that of several related tarantula toxins. The molecular structure of GxTX-1E is similar to those of tarantula toxins that target voltage sensors in Kv channels in that it contains an ICK motif, composed of beta-strands, and contains a prominent cluster of solvent-exposed hydrophobic residues surrounded by polar residues. When compared with the structure of SGTx1, a toxin for which mutagenesis data are available, the residue compositions of the two toxins are distinct in regions that are critical for activity, suggesting that their modes of binding to voltage sensors may be different. Interestingly, the structural architecture of GxTX-1E is also similar to that of JZTX-III, a tarantula toxin that interacts with Kv2.1 with low affinity. The most striking structural differences between GxTX-1E and JZTX-III are found in the orientation between the first and second cysteine loops and the C-terminal region of the toxins, suggesting that these regions of GxTX-1E are responsible for its high affinity.
Lee
Seungkyu
S
Department of Life Science, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea.
Milescu
Mirela
M
Jung
Hyun Ho
HH
Lee
Ju Yeon
JY
Bae
Chan Hyung
CH
Lee
Chul Won
CW
Kim
Ha Hyung
HH
Swartz
Kenton J
KJ
Kim
Jae Il
JI
D000595:Amino Acid Sequence; D000818:Animals; D060829:Arthropod Proteins; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D051669:Shab Potassium Channels / Q000378:metabolism* / Q000502:physiology; D013111:Spider Venoms / Q000737:chemistry* / Q000378:metabolism; D014982:Xenopus laevis
D060829:Arthropod Proteins; C550903:GxTX-1E, Plesiophrictus guangxiensis; D010455:Peptides; D051669:Shab Potassium Channels; D013111:Spider Venoms