The synergetic combination of the distinct properties of azobenzene and bile acid could afford stable tweezer-like conformation with tunable hydrophilic and hydrophobic channels, thus increasing their antimicrobial activity toward both Gram-positive and Gram-negative bacteria, which can be conveniently switched off when the conformation turn back to the extended state. (C) 2016 Elsevier Ltd. All rights reserved.

As the most common fungal pathogen of humans, severe drug resistance has emerged in the clinically isolated Candida albicans, which lead to the urgency to develop novel antifungal agents. Here, four our previously characterized cathelicidins (cathelicidin-BF, Pc-CATH1, Cc-CATH2, Cc-CATH3) were selected and their antifungal activities against C. albicans were evaluated in vitro and in vivo using amphotericin B and LL-37 as control. Results showed that all four cathelicidins could eradicate standard and clinically isolated C. albicans strains with most MIC values ranging from 1 to 16 μg/ml, in less than 0.5 h revealed by time-kill kinetic assay. Four peptides only exhibited slight hemolytic activity with most HC50 > 200 μg/ml, and retained potent anti-C. albicans activity at salt concentrations below and beyond physiological level. In animal experiment, 50 mg/kg administration of the four cathelicidins could significantly reduce the fungal counts in a murine oral candidiasis model induced by clinically isolated C. albicans. The antibiofilm activity of cathelicidin-BF, the most potent among the five peptides was evaluated, and result showed that cathelicidin-BF strongly inhibited C. albicans biofilm formation at 20 μg/ml. Furthermore, cathelicidin-BF also exhibited potent anti-C. albicans activity in established biofilms as measured by metabolic and fluorescent viability assays. Structure-function analyses suggest that they mainly adopt an α-helical conformations, which enable them to act as a membrane-active molecule. Altogether, the four cathelicidins display great potential for antifungal agent development against candidiasis.

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.