Antimicrobial Peptides: Insights into Membrane Permeabilization, Lipopolysaccharide Fragmentation and Application in Plant Disease Control

Abstract

The recent increase in multidrug resistance against bacterial infections has become a major concern to human health and global food security. Synthetic antimicrobial peptides (AMPs) have recently received substantial attention as potential alternatives to conventional antibiotics because of their potent broad-spectrum antimicrobial activity. These peptides have also been implicated in plant disease control for replacing conventional treatment methods that are polluting and hazardous to the environment and to human health. Here, we report de novo design and antimicrobial studies of VG16, a 16-residue active fragment of Dengue virus fusion peptide. Our results reveal that VG16KRKP, a non-toxic and non-hemolytic analogue of VG16, shows significant antimicrobial activity against Gram-negative E. coli and plant pathogens X. oryzae and X. campestris, as well as against human fungal pathogens C. albicans and C. grubii. VG16KRKP is also capable of inhibiting bacterial disease progression in plants. The solution-NMR structure of VG16KRKP in lipopolysaccharide features a folded conformation with a centrally located turn-type structure stabilized by aromatic-aromatic packing interactions with extended N- and C-termini. The de novo design of VG16KRKP provides valuable insights into the development of more potent antibacterial and antiendotoxic peptides for the treatment of human and plant infections.

Mode of Action of a Designed Antimicrobial Peptide: High Potency against Cryptococcus neoformans

“…However, vesicles composed of POPC with 40% cholesterol, that mimic the mammalian cell membrane, demonstrated a negligible amount (~9%) of leakage at the same concentration of peptide. These results further support the fact that the VG16KRKP peptide is highly selective and is nontoxic toward mammalian membranes, which is consistent with our previous study (23). Further, 31 P solidstate NMR spectra of POPC LUVs in the presence of physiological cholesterol concentration (~40%) showed no distortion of the lamellar phase line shape and absence of isotropic peak at 0 ppm even in the presence of VG16KRKP upto 4 mol % concentration.…”

“…7 D). A2, however, still contributes to the hydrophobic interactions as seen in the LPS bound structure (23). Taken together, the hydrophobic hub of VG16KRKP formed in the presence of LPS or C. neoformans cells consisted of A2-W5-L11-F12 or A2-W5-F12, respectively.…”

“…This data suggests that the peptide has similar structural arrangement in both environments where the hydrophobic interaction between W5 and F12 seems to be the driving force, playing a major role in stabilization of the peptides on the membrane interface. However, a marked difference in the orientation of the L11 side chain in the two environments might have an implication in preferential stabilization of the folded conformation in LPS, thus leading to an increase in membrane disruption abilities, as seen in the case of Gram-negative bacteria (23). A lack of stable hydrophobic triad composed of W5-L11-F12 in live C. neoformans cell indicated that the peptide is less stable in the C. neoformans environment that supports a lower efficiency in mediating membrane disruption, possibly due to the presence of a polysaccharide capsule and cell wall in C. neoformans (50).…”

“…In an earlier report a nontoxic and nonhemolytic 16-residue AMP, VG16KRKP (VARGWKRKCPLFGKGG) was designed using first principles; the peptide showed potential activity against Gramnegative plant pathogenic bacteria as well as opportunistic fungal pathogens such as Candida albicans and Cryptococcus neoformans. Mode of action of the peptide against Gram-negative bacteria was elucidated from a structural aspect based on solution NMR structure of the peptide in lipopolysaccharide (LPS), a chief component of the outer membrane of Gram-negative bacteria (23). However, its mode of antifungal action remained unexplored.…”

Random peptide mixtures as new crop protection agents

“…The chemical control options to cope with bacterial diseases in agriculture are limited, and the strategies available for their management are often inadequate (Gitaitis and Walcott, 2007). To date, chemical control of bacterial plant diseases in the field predominantly relies on copper (Cu)‐based bactericides (Datta et al ., 2015). These products, however, possess limited efficacy.…”