A Fungal Defensin Inhibiting Bacterial Cell-Wall Biosynthesis with Non-Hemolysis and Serum Stability.

Sudong Qi,Bin Gao,Shunyi Zhu

doi:10.3390/jof8020174

Abstract

Defensins are a class of cationic disulfide-bridged antimicrobial peptides (AMPs) present in many eukaryotic organisms and even in bacteria. They primarily include two distinct but evolutionarily related superfamilies (cis and trans). Defensins in fungi belong to the members of the cis-superfamily with the cysteine-stabilized α-helical and β-sheet fold. To date, many fungal defensin-like peptides (fDLPs) have been found through gene mining of the genome resource, but only a few have been experimentally characterized. Here, we report the structural and functional characterization of Pyronesin4 (abbreviated as Py4), a fDLP previously identified by genomic sequencing of the basal filamentous ascomycete Pyronema confluens. Chemically, synthetic Py4 adopts a native-like structure and exhibits activity on an array of Gram-positive bacteria including some clinical isolates of Staphylococcus and Staphylococcus warneri, a conditioned pathogen inhabiting in human skin. Py4 markedly altered the bacterial morphology and caused cytoplasmic accumulation of the cell-wall synthesis precursor through binding to the membrane-bound Lipid II, indicating that it works as an inhibitor of cell-wall biosynthesis. Py4 showed no hemolysis and high mammalian serum stability. This work identified a new fungal defensin with properties relevant to drug exploration. Intramolecular epistasis between mutational sites of fDLPs is also discussed.

Highlights

IntroductionAs the effectors of innate immunity in multicellular organisms, antimicrobial peptides (AMPs) establish the first-line defense in the fight against infections from a variety of microorganisms such as bacteria, fungi, viruses, and protozoa [1,2]
Some antimicrobial peptide (AMP) work as a metabolic inhibitor to interact with non-membrane bacterial targets such as Lipid II, outer membrane proteins, and intracellular components (e.g., DNA and proteins) to inhibit their growth [4,6,7]
AMPs markedly differ in sequence and structure and are roughly divided into three major categories on the basis of their amino acid composition and structural types: (1) Linear α-helical AMPs that adopt a helical configuration when contacting microbial membrane, e.g., cecropins from insect hemolymph [8], magainins from frog skins [2], and LL-37 from human neutrophils [9]; (2) Specific amino acid-rich linear AMPs that often lack a defined secondary structure (e.g., PR-39 from pigs [10] and metchnikowin and drosocin from Drosophila [11]); and (3) Disulfide-containing AMPs with a distinct structure stabilized by disulfide bridges (e.g., Protegrin-1 (PG-1) from pigs [12] and defensins from plants, animals, and humans [13]

Summary

Introduction

As the effectors of innate immunity in multicellular organisms, antimicrobial peptides (AMPs) establish the first-line defense in the fight against infections from a variety of microorganisms such as bacteria, fungi, viruses, and protozoa [1,2]. Due to their evolutionary success as host defense molecules across the history of multicellular organisms and less susceptibility to microbial resistance, AMPs have been considered as promising alternatives to conventional antibiotics in the age of resistance [2,3,4]. AMPs markedly differ in sequence and structure and are roughly divided into three major categories on the basis of their amino acid composition and structural types: (1) Linear α-helical AMPs that adopt a helical configuration when contacting microbial membrane, e.g., cecropins from insect hemolymph [8], magainins from frog skins [2], and LL-37 from human neutrophils [9]; (2) Specific amino acid-rich linear AMPs that often lack a defined secondary structure (e.g., PR-39 from pigs [10] and metchnikowin and drosocin from Drosophila [11]); and (3) Disulfide-containing AMPs with a distinct structure stabilized by disulfide bridges (e.g., Protegrin-1 (PG-1) from pigs [12] and defensins from plants, animals, and humans [13]

Methods

Results

Discussion

Conclusion