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The structure of spider toxin huwentoxin-II with unique disulfide linkage: Evidence for structural evolution

¹ Life Science College, Peking University, Beijing 100871, People's Republic of China
² Life Science College, Hunan Normal University, Changsha 410081, People's Republic of China

Reprint requests to: Song-Ping Liang, Life Science College, Hunan Normal University, Changsha 410081, People's Republic of China; e-mail: liangsp{at}public.cs.hu.cn; fax: 86731-8861304.

The three-dimensional structure of huwentoxin-II (HWTX-II), an insecticidal peptide purified from the venom of spider Selenocosmia huwena with a unique disulfide bond linkage as I-III, II-V, and IV-VI, has been determined using 2D ¹H-NMR. The resulting structure of HWTX-II contains two ß-turns (C4-S7 and K24-W27) and a double-stranded antiparallel ß-sheet (W27-C29 and C34-K36). Although the C-terminal double-stranded ß-sheet cross-linked by two disulfide bonds (II-V and IV-VI in HWTX-II, II-V and III-VI in the ICK molecules) is conserved both in HWTX-II and the ICK molecules, the structure of HWTX-II is unexpected absence of the cystine knot because of its unique disulfide linkage. It suggests that HWTX-II adopts a novel scaffold different from the ICK motif that is adopted by all other spider toxin structures elucidated thus far. Furthermore, the structure of HWTX-II, which conforms to the disulfide-directed ß-hairpin (DDH) motif, not only supports the hypothesis that the ICK is a minor elaboration of the more ancestral DDH motif but also suggests that HWTX-II may have evolved from the same structural ancestor.

Keywords: Huwentoxin-II; spider toxin; three-dimensional structure; disulfide bond; inhibitor cystine knot motif; disulfide-directed ß-hairpin; two-dimensional NMR

Abbreviations: HWTX-II, huwentoxin-II • 2D NMR, two dimensional nuclear magnetic resonance • COSY, correlation spectroscopy • DQF-COSY, double-quantum-filtered COSY • NOESY, nuclear Overhauser effect spectroscopy • TOCSY, total correlated spectroscopy • NOE, nuclear Overhauser effect • RMS, root mean square • ICK, inhibitor cystine knot, DDH, disulfide-directed ß-hairpin

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