Structural comparisons of κ-HXTX-Hv1c and ω-HXTX-Hv1a. (A) Comparison of the primary structures of κ-HXTX-Hv1c and ω-HXTX-Hv1a. Identities are boxed and shaded orange while the conserved cysteines that form the cystine-knot motif in each toxin are coloured red. (B) Richardson representation of the 3D structure of κ-HXTX-Hv1c (PDB accession code 1DL0; ) and (C) ω-HXTX-Hv1a (PDB accession code 1AXH; ). Disulfide bonds are shown as orange tubes. The inter-cystine loops and the N- and C-termini are labelled. (D) Stereo-view of an overlay of the 3D structures of κ-HXTX-Hv1c (dark blue with light-blue disulfide bonds) and ω-HXTX-Hv1a (raspberry with light-salmon disulfide bonds). The structural alignment, which was automatically generated by DaliLite , yielded a root mean square deviation of 2.4 Å over the backbone atoms of the 28 aligned residues (Ala1–Ala11, Pro15–Pro18, Ser21–Asn27, and Gly28–Arg33 in κ-HXTX-Hv1c versus Pro2–Pro12, Asn16–Ser19, Ser21–Asn27, and Thr32–Asp37). The inter-cystine loops and the N-terminus are labelled. Figures generated using MacPyMOL .