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Review
. 2019 Feb 19;6(1):29.
doi: 10.3390/medicines6010029.

Medicinal Potentialities of Plant Defensins: A Review with Applied Perspectives

Nida Ishaq  1 , Muhammad Bilal  2 , Hafiz M N Iqbal  3
Affiliations
Review

Medicinal Potentialities of Plant Defensins: A Review with Applied Perspectives

Nida Ishaq et al. Medicines (Basel). .

Abstract

Plant-based secondary metabolites with medicinal potentialities such as defensins are small, cysteine-rich peptides that represent an imperative aspect of the inherent defense system. Plant defensins possess broad-spectrum biological activities, e.g., bactericidal and insecticidal actions, as well as antifungal, antiviral, and anticancer activities. The unique structural and functional attributes provide a nonspecific and versatile means of combating a variety of microbial pathogens, i.e., fungi, bacteria, protozoa, and enveloped viruses. Some defensins in plants involved in other functions include the development of metal tolerance and the role in sexual reproduction, while most of the defensins make up the innate immune system of the plants. Defensins are structurally and functionally linked and have been characterized in various eukaryotic microorganisms, mammals, plants, gulls, teleost species of fish, mollusks, insect pests, arachnidan, and crustaceans. This defense mechanism has been improved biotechnologically as it helps to protect plants from fungal attacks in genetically modified organisms (GMO). Herein, we review plant defensins as secondary metabolites with medicinal potentialities. The first half of the review elaborates the origin, structural variations, and mechanism of actions of plant defensins. In the second part, the role of defensins in plant defense, stress response, and reproduction are discussed with suitable examples. Lastly, the biological applications of plant defensins as potential antimicrobial and anticancer agents are also deliberated. In summary, plant defensins may open a new prospect in medicine, human health, and agriculture.

Keywords: antimicrobial and anticancer activity; defensins; innate immunity; medicine; plant defense; secondary metabolites.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(A) Three-dimensional structure of defensins of plant, invertebrate (insect and mollusk), and vertebrate (mammalian) origin. Structures were downloaded from the protein data bank (http://www.rcsb.org/pdb; PDB accession ID numbers: MGD-1: 1FJN, defensin A: 1ICA, drosomycin: 1MYN, Rs-AFP1: 1AYJ, HNP-3: 1DFN, HBD-2: 1FD3, RTD-1: 1HVZ). Pictures were generated using Rasmol software. The α-helices and β-sheets are shown in yellow and red, respectively. (B) The amino acid sequence of mature Rs-AFP1 and 2. Dashes indicate identical amino acid residues. Connecting lines between cysteine residues represent disulfide bonds, while the spiral and arrows indicate the location of the α-helix and β-strands, respectively. Adapted from Thomma et al. [5], with permission from Springer Nature. Copyright (2002) Springer-Verlag.
Figure 2
Figure 2
Three-dimensional structural conformation of six antifungal plant defensins (adopted from Lacerda et al. [3], an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY)).
Figure 3
Figure 3
Schematic overview of the proposed mechanisms of action of the plant defensins. (A) RsAFP1 and RsAFP2; (B) Psd1; (C) MsDef1; (D) MtDef4; (E) NaD1. Reprinted from Vriens et al. [24], an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/). Copyright (2014) the authors, Licensee MDPI, Basel, Switzerland.
Figure 4
Figure 4
Combined overlay of the light microscopical analysis at 20× magnification and the cell permeabilization assay conducted on B. cinerea grown in the presence of Hc-AFPs for 48 h at 23 °C. (A) Control, (B) Hc-AFP1 25 μg/mL, (C and D) Hc-AFP2 15 μg/mL, (E) Hc-AFP3 25 μg/mL, (F) Hc-AFP4 18 μg/mL. The yellow fluorescence indicates a compromised membrane and the black arrows indicate structures that are leaking their cellular content into the surrounding medium. Adapted from De Beer and Vivier [31], an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0). Copyright (2011) the authors, licensee BioMed Central Ltd.
Figure 5
Figure 5
A schematic illustration of glutathione (GSH) biosynthesis and its involvement in chelation and redox control. Adapted from Jozefczak et al. [37], an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/). Copyright (2012) the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
Figure 6
Figure 6
Potential antimicrobial mechanisms of plant defense-based antimicrobial peptides (AMPs) or host defense peptides HDPs.
See this image and copyright information in PMC

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