Exploring the pharmacological potential of promiscuous host-defense peptides: from natural screenings to biotechnological applications

Abstract

In the last few years, the number of bacteria with enhanced resistance to conventional antibiotics has dramatically increased. Most of such bacteria belong to regular microbial flora, becoming a real challenge, especially for immune-depressed patients. Since the treatment is sometimes extremely expensive, and in some circumstances completely inefficient for the most severe cases, researchers are still determined to discover novel compounds. Among them, host-defense peptides (HDPs) have been found as the first natural barrier against microorganisms in nearly all living groups. This molecular class has been gaining attention every day for multiple reasons. For decades, it was believed that these defense peptides had been involved only with the permeation of the lipid bilayer in pathogen membranes, their main target. Currently, it is known that these peptides can bind to numerous targets, as well as lipids including proteins and carbohydrates, from the surface to deep within the cell. Moreover, by using in vivo models, it was shown that HDPs could act both in pathogens and cognate hosts, improving immunological functions as well as acting through multiple pathways to control infections. This review focuses on structural and functional properties of HDP peptides and the additional strategies used to select them. Furthermore, strategies to avoid problems in large-scale manufacture by using molecular and biochemical techniques will also be explored. In summary, this review intends to construct a bridge between academic research and pharmaceutical industry, providing novel insights into the utilization of HDPs against resistant bacterial strains that cause infections in humans.

Keywords: antimicrobials; host-defense peptides; innate immunity; microbial infections.

Figure 1

An overview of the major structural classes of host-defense peptides including (A) α-helices, (B) β-sheets, (C) a mixture of α-helices/β-sheets structures, (D) cyclic, and (E) extended structures. Disulfide bonds are represented in ball and stick.

Figure 2

Three-dimensional structures of plant antimicrobial peptides. (A) Defensin – Vigna radiata defensin-2, (B) Thionin – Viscum album viscotoxin A3, and (C) Cyclotide – Viola odorata violacin A. Disulfide bonds are represented in ball and stick.

Figure 3

Distribution of host-defense peptides described in human body. The host-defense peptides have a wide distribution in human body, being found mainly in skin, mucous membranes, blood, nervous system, and liver.

Figure 4

A typical “end point” high-throughput screening flow for searching novel host-defense peptides.