In Rhizobium-legume symbiosis, the bacteria are converted into nitrogen-fixing bacteroids.
In many legume species, differentiation of the endosymbiotic bacteria is irreversible,
culminating in definitive loss of their cell division ability. This terminal differentiation
is mediated by plant peptides produced in the symbiotic cells. In Medicago truncatula
more than similar to 700 nodule-specific cysteine-rich (NCR) peptides are involved
in this process. We have shown previously that NCR247 and NCR335 have strong antimicrobial
activity on various pathogenic bacteria and identified interaction of NCR247 with
many bacterial proteins, including FtsZ and several ribosomal proteins, which prevent
bacterial cell division and protein synthesis. In this study we designed and synthetized
various derivatives of NCR247, including shorter fragments and various chimeric derivatives.
The antimicrobial activity of these peptides was tested on the ESKAPE bacteria; Enterococcus
faecalis, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas
aeruginosa, and Escherichia coli as a member of Enterobacteriaceae and in addition
Listeria monocytogenes and Salmonella enterica. The 12 amino acid long C-terminal
half of NCR247, NCR247C partially retained the antimicrobial activity and preserved
the multitarget interactions with partners of NCR247. Nevertheless NCR247C became
ineffective on S. aureus, P. aeruginosa, and L. monocytogenes. The chimeric derivatives
obtained by fusion of NCR247C with other peptide fragments and particularly with a
truncated mastoparan sequence significantly increased bactericidal activity and altered
the antimicrobial spectrum. The minimal bactericidal concentration of the most potent
derivatives was 1.6 mu M, which is remarkably lower than that of most classical antibiotics.
The killing activity of the NCR247-based chimeric peptides was practically instant.
Importantly, these peptides had no hemolytic activity or cytotoxicity on human cells.
The properties of these NCR derivatives make them promising antimicrobials for clinical