Previous studies have proved that a novel antioxidant system composed of various antioxidant
peptides (AOPs) exists in the skin of ranid frogs, keeping the redox homeostasis. However, only
a small number of AOPs have been identified so far. Here, a total of 47 cDNA sequences encoding 21
different AOPs belonging to 11 families were cloned from the skin cDNA library of Limnonectes
fragilis. Among them, fragilin-A1 (VKRRGQDCIHGFCSD) and fragilin-B1 (GQFNDKRWIPFG)
were also purified from skin secretions. They were selected with odorranain-Q-Lf (APIRMWYMYRKLTDMEPKPVA),
the newest sequence among all 21 AOPs, to evaluate the antioxidant activities by direct free
radical scavenging and lipid peroxidation inhibition assay. Results demonstrated that all peptides possessed strong DPPH
and ABTS.+ scavenging activities, and effectively inhibited lipid peroxidation in linoleic acid emulsion system during a 7-
day test. No cytotoxic and hemolytic activity against human erythrocytes was observed for the three AOPs. The homology
modeling analysis revealed that they all adopt tertiary structures ideally suited for the key residues to come into contact
with the radicals. Current results reveal the existence of antioxidant system constituted of AOPs in the skin of the L. fragilis,
and furthermore provide excellent templates for the development of novel antioxidant agents.
Keywords: 3D structure, antioxidant peptide, lipid peroxidation inhibition, radical scavenging, ranid frogs.
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