Antimicrobial peptides from hylid and ranin frogs originated from a 150‐million‐year‐old ancestral precursor with a conserved signal peptide but a hypermutable antimicrobial domain

Abstract

The dermal glands of frogs produce antimicrobial peptides that protect the skin against noxious microorganisms and assist in wound repair. The sequences of these peptides are very dissimilar, both within and between species, so that the 5000 living anuran frogs may produce ≈ 100 000 different antimicrobial peptides. The antimicrobial peptides of South American hylid frogs are derived from precursors, the preprodermaseptins, whose signal peptides and intervening sequences are remarkably conserved, but their C‐terminal domains are markedly diverse, resulting in mature peptides with different lengths, sequences and antimicrobial spectra. We have used the extreme conservation in the preproregion of preprodermaseptin transcripts to identify new members of this family in Australian and South American hylids. All these peptides are cationic, amphipathic and α‐helical. They killed a broad spectrum of microorganisms and acted in synergy. 42 preprodermaseptin gene sequences from 10 species of hylid and ranin frogs were analyzed in the context of their phylogeny and biogeography and of geophysical models for the fragmentation of Gondwana to examine the strategy that these frogs have evolved to generate an enormous array of peptide antibiotics. The hyperdivergence of modern antimicrobial peptides and the number of peptides per species result from repeated duplications of a ≈ 150‐million‐year‐old ancestral gene and accelerated mutations of the mature peptide domain, probably involving a mutagenic, error‐prone, DNA polymerase similar to Escherichia coli Pol V. The presence of antimicrobial peptides with such different structures and spectra of action represents the successful evolution of multidrug defense by providing frogs with maximum protection against infectious microbes and minimizing the chance of microorganisms developing resistance to individual peptides. The hypermutation of the antimicrobial domain by a targeted mutagenic polymerase that can generate many sequence changes in a few steps may have a selective survival value when frogs colonizing a new ecological niche encounter different microbial predators.

Predicted Disease Susceptibility in a Panamanian Amphibian Assemblage Based on Skin Peptide Defenses

“…Studies of preserved museum specimens have found the earliest B. dendrobatidis infection in X. laevis from South Africa in 1938, and enzootic infections were found in nondeclining populations in South Africa (Weldon et al, 2004). Antimicrobial peptide defenses may evolve more readily than components of the adaptive immune system (Zasloff, 2002;Vanhoye et al, 2003). Rapid peptide variation may result from error-prone DNA polymerases (Vanhoye et al, 2003).…”

“…Antimicrobial peptide defenses may evolve more readily than components of the adaptive immune system (Zasloff, 2002;Vanhoye et al, 2003). Rapid peptide variation may result from error-prone DNA polymerases (Vanhoye et al, 2003). As disease advances through Panama, there is the opportunity to study this strong selection pressure on the evolution of peptide immune defenses.…”

“…Natural mixtures of skin peptides are also active (Rollins-Smith et al, 2002b;Woodhams et al, 2006), and this may be more relevant to the natural immune defense of amphibians given that some peptides may act in synergy to inhibit pathogen growth (Westerhoff et al, 1995;Rollins-Smith et al, 2002a). Anuran species show significant variation in the number, structure, and antimicrobial activity of skin peptides (Vanhoye et al, 2003;Apponyi et al, 2004;Conlon et al, 2004).…”

Identification of Miscellaneous Peptides from the Skin Secretion of the European Edible Frog, Pelophylax kl. Esculentus

“…These highly-efficient host-defence compounds that are secreted from the skins of amphibians are attracting ever-increasing scientific attention, as it seems that they may be good templates for the development of new antibiotics designed to combat the emergence of pathogens that are resistant to conventional antibiotics. As many studies have shown, amphibian skin secretions not only produce potent broad-spectrum antimicrobial peptides, but also a number of peptides that have very similar structures and biological activities to mammalian neuropeptides and hormones, such as the bombesins, bradykinins and tachykinins [1][2]. In early research, hundreds or even thousands of amphibians were sacrificed to obtain enough material for biological and chemical analyses, though as modern methods and technologies have developed, this killing has become unnecessary.…”

Skin micro-organs from several frog species secrete a repertoire of powerful antimicrobials in culture

“…3 These secretions not only produce large amounts of biologically active peptides that are similar to mammalian neuropeptides and hormones, but they also contain a rich arsenal of broad-spectrum, cytolytic antimicrobial peptides. 4,5 Their high degree of chemical complexity is evidenced by the fact that they contain proteins, peptides, biogenic amines, alkaloids and other as yet uncharacterized biochemicals. Interestingly, peptides have o5 kDa molecular mass are the predominant molecules in the secretions of many frogs, 6 Five thousand living anuran frog species may produce about 100 000 different antimicrobial peptides.…”