Abstract
Abundant biologically active peptides have been discovered from frog skin secretions, a rich natural source of bioactive compounds with great potential in drug discovery. In this study, three Caeridin peptides, namely, Caeridin-1, S5-Caeridin-1, and Caeridin-a1, were discovered from the skin secretion of the Australian White's tree frog, Litoria caerulea, for the first time, by means of combining transcriptomic and peptidomic analyses. It also represents the first report on bioactive Caeridins since this family of peptides was initially studied 20 years ago. Chemically synthetic versions of each natural Caeridin demonstrated promising bioactivities either on rat smooth muscles or against microbial growth. Specifically, Caeridin-1 produced contraction of rat bladder smooth muscle, while S5-Caeridin-1 induced relaxation of rat ileum smooth muscle, both at nanomolar concentrations. Moreover, Caeridin-a1 was shown to potently inhibit the growth of the planktonic Gram-positive bacteria Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), and Enterococcus faecalis (E. faecalis), the Gram-negative bacterium, Escherichia coli (E. coli), and the yeast, Candida albicans (C. albicans). The discovery of these Caeridins may induce further intensive and systematic studies of frog skin peptides to promote the discovery of natural templates as lead compounds for drug discovery and therapeutic application.
Highlights
In recent years, peptide and peptide-based drugs have been developing fast and have pioneered an essential area in the pharmaceutical industry [1]
Recent trends suggest that the application of therapeutic peptides is becoming more popular, and it has extended to the treatment of many diseases, such as infection, cancer, enzyme deficiency disorders, protein-dysfunction disorders, and even genetic and degenerative diseases [2]
We report the isolation and structural characterisation of Caeridin-1 and two novel Caeridins from the skin secretion of L. caerulea, which were obtained through an ecofriendly method described previously [12], using parallel transcriptomic and peptidomic analyses, as well as through examining their biological activities using synthetic versions in a variety of bioassays
Summary
Peptide and peptide-based drugs have been developing fast and have pioneered an essential area in the pharmaceutical industry [1]. Peptides and proteins contained in these secretions have been considered to play different but important roles in regulating frogs’ physiological functions and defense against predators and microorganisms. With the observed global decline in the frog population during the 1980s, including species extinction, it became apparent that this potentially valuable natural resource needed environmental protection and animal conservation to ensure peptide discovery and acquisition from these natural products could continue and play a role in the future development of novel therapeutic peptides [7, 8]
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