Antimicrobial peptides from the skin secretions of the New World frogs Lithobates capito and Lithobates warszewitschii (Ranidae)

Taxonomic revisions within the anuran family Ranidae have established the genus Lithobates that currently comprises 49 species of frogs from the New World. Peptidomic analysis, using reversed-phase HPLC with on-line detection by electrospray mass spectrometry, has led to the identification of multiple antimicrobial peptides in norepinephrine-stimulated skin secretions of the North American frog Lithobates capito and the Central American frog Lithobates warszewitschii. Structural characterization of the peptides demonstrated that the L. capito secretions contained brevinin-1 (1), esculentin-1 (1), esculentin-2 (1), ranatuerin-2 (3), and temporin (2) peptides. L. warszewitschii secretions contained brevinin-1 (1), esculentin-2 (1), ranatuerin-2 (2), and temporin (1) peptides. Values in parentheses indicate number of peptides in each family. Temporin-CPa from L. capito, with the atypical structure IPPFIKKVLTTVF·NH₂, also showed atypical growth-inhibitory activity having greater potency against Escherichia coli (MIC = 25 μM) and Candida albicans (MIC = 25 μM) than against Staphylococcus aureus (MIC = 50 μM). Phylogenetic analysis based upon the amino acid sequences of 37 ranatuerin-2 peptides from 17 species belonging to the genus Lithobates provides support for currently accepted taxonomic relationships. L. capito is sister-group to Lithobates sevosus in a clade that also contains Lithobates areolatus, and Lithobates palustris. L. warszewitschii is most closely related to the Central American species Lithobates tarahumarae and Lithobates vaillanti.