Determination of the secondary structure of selected melittin analogues with different haemolytic activities

Abstract

In earlier studies, we have reported that minor modifications in the amino acid sequence of melittin result in dramatic changes in its biological activity. In the current study, we have investigated the secondary structure of melittin analogues with either increased or decreased haemolytic activity in order to further our understanding of the structural features involved in the binding and/or insertion of peptides into a phospholipid membrane from solution. This was accomplished by analysing the c.d. spectra of the analogues in solutions of various ionic strength and, separately, in the presence of micelles. These studies permit the assessment of the effect of small sequence modifications (i.e. single amino acid omission or substitution) on the self-association-induced secondary structure of melittin in aqueous solution, as well as its binding affinity to micelles. It was found that amphipathicity, as well as interchain distances and the orientation of hydrophobic residues, were involved in the induction of stabilized structures.

Antimicrobial peptides: New candidates in the fight against bacterial infections

“…For example, substitution of lysine in the hydrophobic N-terminal part of melittin decreases the hydrophobic moment of the peptide and results in the loss of both antimicrobial and hemolytic activity. 107 Cytotoxicity studies of magainin and PGLa analogue peptides produce similar results. 108 In addition to whole cell studies, the loss of antibacterial selectivity due to enhanced amphipathicity was confirmed in lipid model systems where the increase in the permeabilizing efficiency of the peptides is more pronounced in their interaction with neutral phospholipid vesicles.…”

Studies on the Mode of Action of the Antifungal Hexapeptide PAF26

“…Mel.subK7I is an analog with a single Lys-to-Ile substitution at position 7 ( Table 1) that results in reduced interaction with membranes and reduced toxicity to red blood cells, as measured by its hemolytic properties (22). Surprisingly, mel.subK7I initiated P. digitatum permeabilization at concentrations very similar to those of PAF26 and melittin (0.5 to 1 M) (Fig.…”

Inhibition of a plant virus infection by analogs of melittin.

“…5D). At the micromolar concentrations of peptides used in these studies, both melittin and subK7I showed a random coil conformation in the absence of TMV RNA (15). As shown in Fig.…”

“…5D, in the presence of TMV RNA melittin folded into an a-helical conformation, while subK7I adopted a distorted ,3-sheet. As mentioned above, such variations in folding may be related to the differences observed between the antiviral activities of melittin and subK7I, as seen in earlier structure-activity relationship studies with melittin derivatives (15,16).…”

“…Since Lys-7 of melittin lies in a homologous position as the critical Asp-77 and is in a region of similar amino acid sequences in melittin and TMV CP (Fig. 1), melittin and analogs of melittin described earlier as having a single substitution at position 7 (15,16) were tested for their ability to reduce the infectivity of TMV.…”