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

Abstract

Polycationic peptides may present their C-termini in either amidated or acidic form; however, the effects of these conformations on the mechanisms of interaction with the membranes in general were not properly investigated up to now. Protonectarina-MP mastoparan with an either amidated or acidic C-terminus was utilized to study their interactions with anionic and zwitterionic vesicles, using measurements of dye leakage and a combination of H/D exchange and mass spectrometry to monitor peptide-membrane interactions. Mast cell degranulation, hemolysis and antibiosis assays were also performed using these peptides, and the results were correlated with the structural properties of the peptides. The C-terminal amidation promotes the stabilization of the secondary structure of the peptide, with a relatively high content of helical conformations, permitting a deeper interaction with the phospholipid constituents of animal and bacterial cell membranes. The results suggested that at low concentrations Protonectarina-MP interacts with the membranes in a way that both terminal regions remain positioned outside the external surface of the membrane, while the α-carbon backbone becomes partially embedded in the membrane core and changing constantly the conformation, and causing membrane destabilization. The amidation of the C-terminal residue appears to be responsible for the stabilization of the peptide conformation in a secondary structure that is richer in α-helix content than its acidic congener. The helical, amphipathic conformation, in turn, allows a deeper peptide-membrane interaction, favoring both biological activities that depend on peptide structure recognition by the GPCRs (such as exocytosis) and those activities dependent on membrane perturbation (such as hemolysis and antibiosis).

Lipid-packing perturbation of model membranes by pH-responsive antimicrobial peptides

“…From the structural point of view, the C-terminus amidation was shown by NMR to provide an extra hydrogen bonding in Eumenine mastoparan-AF (EMP-AF-NH 2 ) compared with the non-amidated analog (Sforça et al 2004). Similar observations were carried out for Protonectarina-MP using hydrogen deuterium exchange and mass spectrometry (da Silva et al 2014). This helical stabilizing effect was also observed in the less frequent post-translational modification in the N-terminus, for instance its acetylation.…”

Mastoparan is a membranolytic anti-cancer peptide that works synergistically with gemcitabine in a mouse model of mammary carcinoma

“…Therefore, the differences in Mastoparan-mediated membrane lysis as well as increased propensity to adopt the active conformation of the peptide might thus explain why C-terminal amidation alters both potency as well as the mechanism of Mastoparan-mediated cytotoxicity. Consistent with this, da Silva et al recently found that C-terminal amidation of related but distinct Mastoparans promoted deeper peptide-membrane interactions[23]. …”

Modification Targeting the “Rana Box” Motif of a Novel Nigrocin Peptide From Hylarana latouchii Enhances and Broadens Its Potency Against Multiple Bacteria

“…Previously, C-terminal amidation of PMAP-23 was reported to possess more rapid bactericidal kinetics and more helical structure of it in the bacterial membrane environment than the same concentration of PMAP-23C because of the increased cationic charge (Kim et al, 2011). In addition, the amidation of C-terminal residue might be responsible for the stabilization of the secondary helical structure of mastoparans that is richer than its congener (da Silva et al, 2014). Meanwhile, Irazazabal et al (2016) suggested that the increase of net charge by +1 of [I 5 , R 8 ] MP-amide might compensate and overcome the lower level of coil-to-α-helix transition compared with the non-amidated peptide.…”