1. Peptidomic analysis of skin secretions supports separate species status for the tailed frogs, Ascaphus truei and Ascaphus montanus
J Michael Conlon, Catherine R Bevier, Laurent Coquet, Jérôme Leprince, Thierry Jouenne, Hubert Vaudry, Blake R Hossack Comp Biochem Physiol Part D Genomics Proteomics. 2007 Jun;2(2):121-5. doi: 10.1016/j.cbd.2007.01.003. Epub 2007 Jan 30.
The tailed frog Ascaphus truei Stejneger, 1899 is the most primitive extant anuran and the sister taxon to the clade of all other living frogs. The species occupies two disjunct ranges in the Northwest region of North America: the Cascade Mountains and coastal area from British Columbia to Northern California, and an inland range in the northern Rocky Mountains and the Blue and Wallowa mountains. A previous study led to the isolation of eight peptides with antimicrobial activity (termed the ascaphins) from skin secretions of A. truei from the coastal range. The present study has used peptidomic analysis to identify the products of orthologous ascaphin genes in electrically-stimulated skin secretions from inland range specimens. Structural characterization of the peptides demonstrated that ascaphins from the inland range contained the following amino acid substitutions compared with orthologs from the coastal range frogs: ascaphin-1 (Ala(12)-->Glu), ascaphin-3 (Asp(4)-->Glu), ascaphin-4 (Ala(19)-->Ser), ascaphin-5 (Lys(12)-->Thr), and ascaphin-7 (Gly(8)-->Ser and Ser(20)-->Asn). Orthologs of ascaphins-2, -6, and -8 were not identified but a paralog of ascaphin-5, identical to ascaphin-5 from coastal range frogs, was found. The data support the claims, derived from analysis of the nucleotide sequences of mitochondrial genes, that the inland populations of the tailed frog should be recognized as a distinct species, the Rocky Mountain tailed frog Ascaphus montanus and that the divergence of the species from A. truei probably occurred in the late Miocene (approximately 10 Mya).
2. The ascaphins: a family of antimicrobial peptides from the skin secretions of the most primitive extant frog, Ascaphus truei
J Michael Conlon, Agnes Sonnevend, Carlos Davidson, D David Smith, Per F Nielsen Biochem Biophys Res Commun. 2004 Jul 16;320(1):170-5. doi: 10.1016/j.bbrc.2004.05.141.
The tailed frog Ascaphus truei occupies a unique position in phylogeny as the most primitive extant anuran and is regarded as the sister taxon to the clade of all other living frogs. Eight structurally related peptides, termed ascaphins 1-8, were isolated from norepinephrine-stimulated skin secretions of A. truei and were shown to possess differential growth inhibitory activity against Escherichia coli and Staphylococcus aureus. Ascaphins 2-7 may be represented by the consensus amino acid sequence GX2DX2KGAAKX3KTVAX2IANX.COOH whereas ascaphin-1 (GFRDVLKGAAKAFVKTVAGHIAN.NH2) and ascaphin-8 (GFKDLLKGAAKALVKTVLF.NH2) contain a C-terminally alpha-amidated residue. The ascaphins show no appreciable structural similarity with other families of antimicrobial peptides from frog skin but display limited sequence identity with the cationic, amphipathic alpha-helical peptides pandinin 1 and opistoporin 1, isolated from the venoms of African scorpions. Ascaphin-8 shows the highest potency against a range of pathogenic microorganisms but has the greatest haemolytic activity. The data indicate that the host defence strategy of using antimicrobial peptides in skin secretions arose early in the evolution of anurans.
