Esculentin-2PRa

Population declines due to amphibian chytridiomycosis among selected species of ranid frogs from western North America have been severe, but there is evidence that the Oregon spotted frog, Rana pretiosa Baird and Girard, 1853, displays resistance to the disease. Norepinephrine-stimulated skin secretions were collected from a non-declining population of R. pretiosa that had been exposed to the causative agent Batrachochytrium dendrobatidis. Peptidomic analysis led to identification and isolation, in pure form, of a total of 18 host-defense peptides that were characterized structurally. Brevinin-1PRa, -1PRb, -1PRc, and -1PRd, esculentin-2PRa and -PRb, ranatuerin-2PRa, -2PRb, -2PRc, and -2PRe, temporin-PRb and -PRc were identified in an earlier study of skin secretions of frogs from a different population of R. pretiosa known to be declining. Ranatuerin-2PRf, -2PRg, -2PRh, temporin-PRd, -PRe, and -PRf were not identified in skin secretions from frogs from the declining population, whereas temporin-PRa and ranatuerin-2PRd, present in skin secretions from the declining population, were not detected in the current study. All purified peptides inhibited the growth of B. dendrobatidis zoospores. Peptides of the brevinin-1 and esculentin-2 families displayed the highest potency (minimum inhibitory concentration = 6.25-12.5 μM). The study provides support for the hypothesis that the multiplicity and diversity of the antimicrobial peptide repertoire in R. pretiosa and the high growth-inhibitory potency of certain peptides against B. dendrobatidis are important in conferring a measure of resistance to fatal chytridiomycosis.

Population declines due to chytridiomycosis among frogs belonging to the Amerana (Rana boylii) species group from western North America have been particularly severe. Norepinephrine-stimulated skin secretions from the Oregon spotted frog Rana pretiosa Baird and Girard, 1853 were collected from individuals that had been previously infected with the causative agent Batrachochytrium dendrobatidis but had proved resistant to developing chytridiomycosis. These secretions contained a more diverse array of antimicrobial peptides than found in other species from the Amerana group and 14 peptides were isolated in pure form. Determination of their primary structures identified the peptides as esculentin-2PRa and -2PRb; ranatuerin-2PRa, -2PRb, -2PRc, -2PRd, and -2PRe; brevinin-1PRa, -1PRb, -1PRc, and -1PRd; and temporin-PRa, -PRb, and -PRc. The strongly cationic ranatuerin-2PRd and the esculentin-2 peptides, which have not been identified in the secretions of other Amerana species except for the closely related R. luteiventris, showed the highest growth inhibitory potency against microorganisms. The strongly hydrophobic brevinin-1PRd was the most cytotoxic to erythrocytes. Although no clear correlation exists between production of dermal antimicrobial peptides by a species and its resistance to fatal chytridiomycosis, the diversity of these peptides in R. pretiosa may be pivotal in defending the species against environmental pathogens such as B. dendrobatidis.