A family of antimicrobial and immunomodulatory peptides related to the frenatins from skin secretions of the Orinoco lime frog Sphaenorhynchus lacteus (Hylidae)

•Three frenatin-related peptides were isolated from Sphaenorhynchus lacteus skin secretions.•Frenatin 2.1S and 2.2S show potent bactericidal activity against MRSA.•Frenatin 2.1S and 2.2S are cytotoxic to lung adenocarcinoma A549 cells.•Frenatin 2.1S and 2.2S enhance production of TNF-α, IL-1β, and IL23 by mouse macrophages.•Frenatin 2.2S inhibits production of IL-10 by lipopolysaccharide-stimulated macrophages. Peptidomic analysis of norepinephrine-stimulated skin secretions of the Orinoco lime tree frog Sphaenorhynchus lacteus (Hylidae, Hylinae) revealed the presence of three structurally related host-defense peptides with limited sequence similarity to frenatin 2 from Litoria infrafrenata (Hylidae, Pelodryadinae) and frenatin 2D from Discoglossus sardus (Alytidae). Frenatin 2.1S (GLVGTLLGHIGKAILG.NH2) and frenatin 2.2S (GLVGTLLGHIGKAILS.NH2) are C-terminally α-amidated but frenatin 2.3S (GLVGTLLGHIGKAILG) is not. Frenatin 2.1S and 2.2S show potent bactericidal activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MIC ≤16μM) but are less active against a range of Gram-negative bacteria. Frenatin 2.1S (LC50=80±6μM) and 2.2S (LC50=75±5μM) are cytotoxic against non-small cell lung adenocarcinoma A549 cells but are less hemolytic against human erythrocytes (LC50=167±8μM for frenatin 2.1S and 169±7μM for 2.2S). Weak antimicrobial and cytotoxic potencies of frenatin 2.3S demonstrate the importance of C-terminal α-amidation for activity. Frenatin 2.1S and 2.2S significantly (P