Genetic analysis of signal peptides in amphibian antimicrobial secretions

Amphibian secretion is an important source of bioactive molecules that naturally protect the skin against noxious microorganisms. Collectively called antimicrobial peptides (AMPs), these molecules have a wide spectrum of action, targeting viruses, bacteria and fungi. Like many membrane and secreted proteins, AMPs have cleavable signal sequences that mediate and translocate the nascent polypeptide chains into the endoplasmic reticulum. Although it is accepted that the signal peptides (SPs) are simple and interchangeable, there is neither sequence nor structure that is conserved among all gene families. They derived from a common ancestor but developed different traits as they adapt to distinct environmental pressures. The aim of this study was to provide an overview of the diversity of SPs of the frog, taking into account reported cDNA sequences and the evolutionary relationship among them. We analysed more than 2000 records that reported the relative abundance, diversity and evolutionary divergence based on the peptide signals of frog AMPs. We conclude that the physical properties of the sequence are more important than the specific peptides in AMP SPs. Since there is significant overlapping among related genera, differences in secretion from different peptide types should be regulated by additional levels, such as posttranscriptional modifications or 5-UTR sequences.