Structural diversity and species distribution of host-defense peptides in frog skin secretions

Abstract

Cationic peptides that adopt an amphipathic α-helical conformation in a membrane-mimetic environment are synthesized in the skins of many frog species. These peptides often display cytolytic activities against bacteria and fungi consistent with the idea that they play a role in the host's system of defense against pathogenic microorganisms, but their importance in the survival strategy of the animal is not clearly understood. Despite the common misconception that antimicrobial peptides are synthesized in the skins of all anurans, the species distribution is sporadic, suggesting that their production may confer some evolutionary advantage to the organism but is not necessary for survival. The low potency of many frog skin antimicrobial peptides is consistent with the hypothesis that cutaneous symbiotic bacteria may provide the major system of defense against pathogenic microorganisms in the environment with antimicrobial peptides assuming a supplementary role in some species.

Antimicrobial peptides from the skin of the Asian frog, Odorrana jingdongensis: De novo sequencing and analysis of tandem mass spectrometry data

“…As shown in Table 3, eight AMPs identified in the present work could be grouped into four known families: Brevinin-1, Brevinin-2, Esculentin-2 and Nigrocin-2 which have been found in many Ranidaes [5]. Antimicrobial and hemolytic activities of the four families from this genus have been well defined [5,10,[13][14][15][17][18][19][20]24], however, their antimicrobial activities against resistant strains have been rarely assessed [19,20].…”

“…S1A), indicating that this type of cleavage may occur at the low consequence. A plausible reason of these unusual cleavages occurring is in the molecular structure itself: a 7-membered disulfide bridge referred to as the 'Rana box' [5] at their Cterminus and no Proline within disulfide loop which is different to previously reported peptides observed unusual cleavages [41][42][43]; moreover, segment sequences within the disulfide loop may be important to the cleavages. For example, more abundance fragment ions generated by the unusual cleavages had been found in Nigrocin-2JDa and Nigrocin-2JDb which contain an acidic peptide segment based on the SpI while the others contain an alkaline peptide segment (Table 3).…”

“…In Collection of Anti-Microbial Peptides database (CAMP, updated on 29th April 2010, http://www.bicnirrh.res.in/antimicrobial/), there are 2867 validated AMPs and 1153 predicted AMPs with antimicrobial sequences [4]. Many AMPs have been identified from skin [5], brain [6] and stomach [7] of Anurans (frogs and toads). Skin secretions from Anurans contain a wide range of compounds with the biological activity.…”

“…Skin secretions from Anurans contain a wide range of compounds with the biological activity. Peptides are the major components of the secretions in many species, and the predominant peptides are often those with antimicrobial activity [5,8].…”

Host defense peptides in skin secretions of Odorrana tiannanensis: Proof for other survival strategy of the frog than merely anti-microbial

“…One explanation for such low potency is the hypothesis that cutaneous symbiotic bacteria may provide the major defense system against pathogens in the habitats of certain frog species [20,21]. In these species, natural selection may have attenuated the potency so that symbiotic cutaneous microbes are able to survive in the antibacterial skin secretions [22,23].…”