κ-Hefutoxin1, a Novel Toxin from the ScorpionHeterometrus fulvipes with Unique Structure and Function IMPORTANCE OF THE FUNCTIONAL DIAD IN POTASSIUM CHANNEL SELECTIVITY

Kellathur N. Srinivasan; Vaithiyalingam Sivaraja; Isabelle Huys; Toru Sasaki; Betty Cheng; Thallampuranam Krishnaswamy S. Kumar; Kazuki Sato; Jan Tytgat; Chin Yu; B. Chia Cheng San; Shoba Ranganathan; H. John Bowie; R. Manjunatha Kini; Ponnampalam Gopalakrishnakone

doi:10.1074/jbc.M111258200

κ-Hefutoxin1, a Novel Toxin from the ScorpionHeterometrus fulvipes with Unique Structure and Function

IMPORTANCE OF THE FUNCTIONAL DIAD IN POTASSIUM CHANNEL SELECTIVITY*

From the ^tOaVenom and Toxin Research Programme, Faculty of Medicine, National University of Singapore, 4 Medical Dr., Singapore 117597, Singapore, the ^tOcDepartment of Chemistry, National Tsing Hua University, Hsinchu, Taiwan, the ^tOdLaboratory of Toxicology, University of Leuven, E. Van Evenstr, 3000 Leuven, Belgium, ^tOfMitsubishi Kasei Institute of Life Sciences, 11 Minamiooya, Machida-shi, Tokyo 194-8511, Japan, ^tOgBioinformatics Centre and Department of Biochemistry, Faculty of Medicine, and the ^tOkDepartment of Biological Sciences, Faculty of Science, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore ^tOhFukuoka Women's University, Kasumigaoka, Higashi-ku, Fukuoka, 813-8529, Japan, the ^tOjDepartment of Chemistry, University of Adelaide, South Australia 5005, Australia, and ⁱDSO National Laboratories, Singapore 118230, Singapore

Abstract

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, κ-hefutoxin1 and κ-hefutoxin2, exhibit no homology to any known toxins. NMR studies indicate that κ-hefutoxin1 adopts a unique three-dimensional fold of two parallel helices linked by two disulfide bridges without any β−sheets. Based on the presence of the functional diad (Tyr⁵/Lys¹⁹) at a distance (6.0 ± 1.0 Å) comparable with other potassium channel toxins, we hypothesized its function as a potassium channel toxin. κ-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 κ-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.

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