Defence peptides in the amphibian immune system

Amphibian skin is a rich source of biologically active compounds, such as amines, complex alkaloids or peptides and proteins which are produced by holocrine-type serous glands, where they are stored and released upon stimulation. In particular, a high number of gene-encoded antimicrobial peptides have been isolated and characterised from amphibian skin secretions, containing 10-50 amino acid residues. Several of these peptides are characterised by posttranslational modifications, such as amidation at the C-terminal end or isomerization of an L-amino acid to the corresponding D-isomer. Here, the structural and functional properties of amphibian antimicrobial peptides, as well as the mechanisms regulating their synthesis are reviewed.