Legume Plant Peptides as Sources of Novel Antimicrobial Molecules Against Human Pathogens

Abstract

Antimicrobial peptides are prominent components of the plant immune system acting against a wide variety of pathogens. Legume plants from the inverted repeat lacking clade (IRLC) have evolved a unique gene family encoding nodule-specific cysteine-rich NCR peptides acting in the symbiotic cells of root nodules, where they convert their bacterial endosymbionts into non-cultivable, polyploid nitrogen-fixing cells. NCRs are usually 30–50 amino acids long peptides having a characteristic pattern of 4 or 6 cysteines and highly divergent amino acid composition. While the function of NCRs is largely unknown, antimicrobial activity has been demonstrated for a few cationic Medicago truncatula NCR peptides against bacterial and fungal pathogens. The advantages of these plant peptides are their broad antimicrobial spectrum, fast killing modes of actions, multiple bacterial targets, and low propensity to develop resistance to them and no or low cytotoxicity to human cells. In the IRLC legumes, the number of NCR genes varies from a few to several hundred and it is possible that altogether hundreds of thousands of different NCR peptides exist. Due to the need for new antimicrobial agents, we investigated the antimicrobial potential of 104 synthetic NCR peptides from M. truncatula, M. sativa, Pisum sativum, Galega orientalis and Cicer arietinum against eight human pathogens, including ESKAPE bacteria. 50 NCRs showed antimicrobial activity with differences in the antimicrobial spectrum and effectivity. The most active peptides eliminated bacteria at concentrations from 0.8 to 3.1 μM. High isoelectric point and positive net charge were important but not the only determinants of their antimicrobial activity. Testing the activity of shorter peptide derivatives against Acinetobacter baumannii and Candida albicans led to identification of regions responsible for the antimicrobial activity and provided insight into their potential modes of action. This work provides highly potent lead molecules without hemolytic activity on human blood cells for novel antimicrobial drugs to fight against pathogens.

Enhanced Antibacterial Activity of Substituted Derivatives of NCR169C Peptide

“…The use of human blood for the hemolysis assay has been authorized by the Regional Hungarian Ethics Committee and approved by the Ethics Review Sector of DG RTD (European Commission) in connection with EK's ERC AdG SymBiotics. The protocol was performed as described by Lima et al [30]. Baseline OD 560 values were determined with cells in TBS buffer, while 0.5% Triton X-100 (Serva) was added to the cells at the same time as NCRs represented 100% of hemolysis.…”

“…For example, the 24-amino-acid-long NCR247 peptide, together with its derivates, displayed promising antimicrobial activity against several bacterial strains including ESKAPE pathogens [28]. A recent publication from our group revealed that among 104 synthetic NCR peptides from M. truncatula, M. sativa, Pisum sativum, Galega orientalis, and Cicer arietinum, almost all cationic peptides displayed a broad antimicrobial spectrum, as well as the effective and rapid killing of ESKAPE bacteria within a minimal bactericidal concentration (MBC) range of 0.8-3.1 µM [30].…”

Innovative Phospholipid Carriers: A Viable Strategy to Counteract Antimicrobial Resistance

“…Antimicrobial peptide-based therapy, suggested by and developed from the multitude of insects, plants, and other organisms that make daily use of them for survival [50][51][52][53], showed a minor insurgence of antibiotic resistance due to the intrinsic multi-modal, multitarget action derived from the more complex structure of these compounds, and a plethora of co-adjuvant properties such as antioxidant, anti-inflammatory, and pro-healing effects [54,55]. However, their application in therapy is restricted because of their side effects, caused by off-target reactions with human epitopes and by the high concentration (derived from their conspicuous molecular weight) at which they need to be administered to exert their properties.…”