kappa-Hefutoxin1, a novel toxin from the scorpion Heterometrus fulvipes with unique structure and function. Importance of the functional diad in potassium channel selectivity.
An important and exciting challenge in the postgenomic era is to understand the functions of newly discovered proteins based on their structures. The main thrust is to find the common structural motifs that contribute to specific functions. Using this premise, here we report the purification, solution NMR, and functional characterization of a novel class of weak potassium channel toxins from the venom of the scorpion Heterometrus fulvipes. These toxins, kappa-hefutoxin1 and kappa-hefutoxin2, exhibit no homology to any known toxins. NMR studies indicate that kappa-hefutoxin1 adopts a unique three-dimensional fold of two parallel helices linked by two disulfide bridges without any beta-sheets. Based on the presence of the functional diad (Tyr(5)/Lys(19)) at a distance (6.0 +/- 1.0 A) comparable with other potassium channel toxins, we hypothesized its function as a potassium channel toxin. kappa-Hefutoxin 1 not only blocks the voltage-gated K(+)-channels, Kv1.3 and Kv1.2, but also slows the activation kinetics of Kv1.3 currents, a novel feature of kappa-hefutoxin 1, unlike other scorpion toxins, which are considered solely pore blockers. Alanine mutants (Y5A, K19A, and Y5A/K19A) failed to block the channels, indicating the importance of the functional diad.
Srinivasan
Kellathur N
KN
Venom and Toxin Research Programme, Faculty of Medicine, National University of Singapore, 4 Medical Dr., Singapore 117597, Singapore.
Sivaraja
Vaithiyalingam
V
Huys
Isabelle
I
Sasaki
Toru
T
Cheng
Betty
B
Kumar
Thallampuranam Krishnaswamy S
TK
Sato
Kazuki
K
Tytgat
Jan
J
Yu
Chin
C
San
B Chia Cheng
BC
Ranganathan
Shoba
S
Bowie
H John
HJ
Kini
R Manjunatha
RM
Gopalakrishnakone
Ponnampalam
P
D000595:Amino Acid Sequence; D000818:Animals; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D015221:Potassium Channels / Q000187:drug effects*; D011487:Protein Conformation; D012605:Scorpions; D017386:Sequence Homology, Amino Acid; D021241:Spectrometry, Mass, Electrospray Ionization; D014118:Toxins, Biological / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology
D015221:Potassium Channels; D014118:Toxins, Biological