Influence of C-Terminal Amidation on the Efficacy of Modelin-5

Abstract

To gain insight into the effects of amidation on the mechanism of membrane interaction, we studied two peptides modelin-5-COOH and modelin-5-CONH(2) and found they exhibit high surface activities (23.2 and 27.1 mN/m, respectively). When they were tested against Escherichia coli, amidation was seen to increase efficacy approximately 10-fold. Our results demonstrated that both peptides adopted low levels of α-helix in solution (<20%); however, in the presence of E. coli lipid extract, modelin-5-CONH(2) had a greater propensity (69%) than modelin-5-COOH (32%) to generate α-helical structure. The binding coefficient for both peptides was ∼10 μM, and the Hill coefficient approximated 1, suggesting that for both peptides the interactions with E. coli membranes were monomeric and comparable in strength. The peptides showed a clear preference for anionic lipid, with monolayer data showing that enhanced levels of helicity were associated with a greater pressure change (∼6 mN/m). Use of fluorescein-phosphatidylethanolamine showed the amidated version was able to generate greater levels of membrane disruption, which was confirmed by thermodynamic analysis. The data would imply that both peptides are able to initially bind to bilayer structures, but upon binding, the amidation stabilizes helix formation. This would be expected to help overcome a key rate-limiting step and generate higher local concentrations of peptide at the bilayer interface, which in turn would be predicted to increase efficacy.

Low pH Enhances the Action of Maximin H5 against Staphylococcus aureus and Helps Mediate Lysylated Phosphatidylglycerol-Induced Resistance

“…It also seems likely that the amide moiety at the C-terminus of MH5 helps promote stabilisation of the peptide's α-helical secondary structure. It is well established that C-terminal amidation provides an extra hydrogen bonding capability that stabilizes amphiphilic α-helix formation by AMPs upon membrane binding, thereby enhancing their membranolytic action and antimicrobial activity 103,104 . Together, these observations could help explain why MH5 appears able to evade some adaptive mechanisms of resistance possessed by S. aureus to combat anionic AMPs and how the peptide targets membranes of the organism 33,105 .…”

The effects of the C-terminal amidation of mastoparans on their biological actions and interactions with membrane-mimetic systems

“…The enhanced potency of inflammatory peptides with amidated Cterminal residues is attributed to the increased positive charge at the N-terminus, which appears to promote the interaction between these peptides and the predominantly negatively-charged bacterial membranes [15][16][17][18]. This aspect facilitates the interaction between the peptides and the cell membrane, leading to membrane permeabilization [19].…”

Piloting the Membranolytic Activities of Peptides with a Self‐organizing Map

“…Overall, protonectin and decoralin showed stronger membranolytic activity on POPC vesicles than on PEPG vesicles, and both peptides exhibited greater activity when amidated at their C termini than their counterparts with free C termini (Table 1); this is in accordance with previous studies on cationic helical AMPs. [25] Deletion of either C-terminal or N-terminal amino acids abolished or strongly reduced the membranolytic activities of the two natural AMPs. In the case of decoralin, deletion of the N terminus had a much stronger effect on the activity on POPC vesicles than deletion of the C terminus.…”