Figure 6. Structural and functional evolution of the pipid defense peptide arsenal.

(A) Evolutionary scenario for the origin and loss of defense peptides and their function along a summarized phylogenetic tree. Numbers along tree branches represent structural changes as mentioned in the legend. (B) Evolutionary trajectory showing structural changes and functional transitions from the ancestral cck gene to the present-day X. laevis xpf-Xl1 gene, encoding the AMP XPF and the HLP xenopsin. Only gene duplication events relevant to functional changes (see text) are indicated. (C) Comparative alignment of levitide-like peptides, X. laevis xenopsin and the vertebrate neurohormones with which it shows evolutionary convergence. The origins of the different peptides are indicated on the right. Amino acids are color-coded as follows: white, hydrophobic; grey, near-neutral; purple, uncharged polar; blue, cationic (basic); red; anionic (acidic).