Fig. 6.

Comparison of the cDNA-encoded precursor sequence of Fla-18, a cysteine-free O1-superfamily conotoxin identified in this work, with the 20 most similar sequences of known O1-conotoxins. A, precursor sequence alignment shows that the organization of the Fla-18 precursor is distinct from that of the precursors of the canonical O1-conotoxins. The mature peptide region of Fla-18 is inserted into the propeptide region, and the C-terminal cysteine-rich region is missing in Fla-18. B, comparison of the cDNA and protein sequences of Fla18 and Qc6.1 shows that the absence of the cysteine-rich region in Fla-18 is caused by a 14-bp deletion in its cDNA sequence, which leads to the premature termination of the coding region.