Sequence logo and codon usage analysis from the Shiva superfamily. (A) Sequence logo  based on alignment of prepropeptides from the Shiva superfamily. There is a much higher level of sequence conservation within the signal peptide than within the propeptide and mature toxin regions. Note, however, that the cysteine residues that form the cystine-knot motif in the mature toxin and the Arg-Arg protease recognition site that terminates the propeptide region are both completely conserved (highlighted in blue and red, respectively). (B) Codon usage for the six-cysteine residues that form the cystine-knot motif. Note the strong bias for TGC at cysteine positions 1, 3, 4, and 6. Shown above the histogram is the disulfide bridge arrangement for the six cysteines as inferred from the 3D structures of ω-HXTX-Hv1a and κ-HXTX-Hv1c.