Abstract
Amphibian skin secretion has great potential for drug discovery and contributes hundreds of bioactive peptides including bradykinin-related peptides (BRPs). More than 50 BRPs have been reported in the last two decades arising from the skin secretion of amphibian species. They belong to the families Ascaphidae (1 species), Bombinatoridae (3 species), Hylidae (9 speices) and Ranidae (25 species). This paper presents the diversity of structural characteristics of BRPs with N-terminal, C-terminal extension and amino acid substitution. The further comparison of cDNA-encoded prepropeptides between the different species and families demonstrated that there are various forms of kininogen precursors to release BRPs and they constitute important evidence in amphibian evolution. The pharmacological activities of isolated BRPs exhibited unclear structure–function relationships, and therefore the scope for drug discovery and development is limited. However, their diversity shows new insights into biotechnological applications and, as a result, comprehensive and systematic studies of the physiological and pharmacological activities of BRPs from amphibian skin secretion are needed in the future.
Highlights
The skin secretions of amphibians have been widely studied over the past several decades
BK is the final product of the kallikrein–kinin system in the mammalian blood system, and is liberated from three types of kininogens: high molecular weight kininogens and low molecular weight kininogens encoded by a single gene, which are found in humans, and T-kininogens found in rats
Regarding the natural roles of these bradykinin-related peptides (BRPs), the hypothesis is that they act as skin defence compounds mediated on the BK receptor of their predators
Summary
The skin secretions of amphibians have been widely studied over the past several decades. Bioactive peptides are predominant and remarkable in amphibian skin secretion as a large amount of antimicrobial peptides, physiological active peptides and neurotransmitter like peptides have been discovered [4,5,6] These peptides are considered to be an important part of their innate immune system, enabling them to have survived predators and infection from microorganisms for millions of years [2]. More than a hundred results are shown if the search term “amphibian and bradykinin” is used through Uniprot Data base (Pubmed access time: 7 December 2014) Whilst this is not a large amount compared to other kinds of skin defence peptides, such as antimicrobial peptides, of which there are nearly 2000 records in the. When compared to BK, a high and varying degree of structural changes occur through four main characteristics: N-terminal extension, C-terminal extension, segment insertion and amino acid substitutions and the cloned cDNAs illustrated by the phenomenon of single copy or multiple tandem copies of mature peptide in a full-length cDNA sequence
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