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

Abstract

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 1 H‐NMR. The resulting structure of HWTX‐II contains two β‐turns (C4‐S7 and K24‐W27) and a double‐stranded antiparallel β‐sheet (W27‐C29 and C34‐K36). Although the C‐terminal double‐stranded β‐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 β‐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.