RV-23, a Melittin-Related Peptide with Cell-Selective Antibacterial Activity and High Hemocompatibility.

RV-23 is a melittin-related antibacterial peptide (MRP) with lower cytotoxicity than either melittin or AR-23, another MRP. The aim of this study was to explore the mechanism of RV- 23's antibacterial selectivity and its hemocompatibility. The results showed that all the peptides exhibited lytic activity against Staphylococcus aureus and Escherichia coli, with RV-23 showing the highest potency. Moreover, RV-23 had lower cytotoxicity than melittin or AR-23 at their minimal inhibitory concentration. In addition, CD experiments showed that melittin, RV-23, and AR-23 all had a typical α-helical structure, and RV-23 had the lowest α-helix content. The structural information showed that RV-23 has the lowest hydrophobicity and highest hydrophobic moment. Because hydrophobicity and α-helix content are believed to correlate with hemolysis, the results indicate that the selective lytic activity against bacteria of RV-23 may be due to its low hydrophobicity and α-helicity, which lead to low cytotoxicity without affecting antibacterial activity. Furthermore, RV-23 did not affect the structure and function of blood components such as red blood cells, platelets, albumin, and the blood coagulation system. In conclusion, RV-23 is a cell-selective antibacterial peptide with high hemocompatibility due to its unique structure.

The effect of cyclization of magainin 2 and melittin analogues on structure, function, and model membrane interactions: implication to their mode of action.

The amphipathic alpha-helical structure is a common motif found in membrane binding polypeptides including cell lytic peptides, antimicrobial peptides, hormones, and signal sequences. Numerous studies have been undertaken to understand the driving forces for partitioning of amphipathic alpha-helical peptides into membranes, many of them based on the antimicrobial peptide magainin 2 and the non-cell-selective cytolytic peptide melittin, as paradigms. These studies emphasized the role of linearity in their mode of action. Here we synthesized and compared the structure, biological function, and interaction with model membranes of linear and cyclic analogues of these peptides. Cyclization altered the binding of melittin and magainin analogues to phospholipid membranes. However, at similar bound peptide:lipid molar ratios, both linear and cyclic analogues preserved their high potency to permeate membranes. Furthermore, the cyclic analogues preserved approximately 75% of the helical structure of the linear peptides when bound to membranes. Biological activity studies revealed that the cyclic melittin analogue had increased antibacterial activity but decreased hemolytic activity, whereas the cyclic magainin 2 analogue had a marked decrease in both antibacterial and hemolytic activities. The results indicate that the linearity of the peptides is not essential for the disruption of the target phospholipid membrane, but rather provides the means to reach it. In addition, interfering with the coil-helix transition by cyclization, while maintaining the same sequence of hydrophobic and positively charged amino acids, allows a separated evaluation of the hydrophobic and electrostatic contributions to binding of peptides to membranes.

Melittin, a metabostatic peptide inhibiting Gs activity.

Some basic amphiphilic peptides are known to directly stimulate heterotrimeric GTP-binding proteins (G proteins). Mastoparan and melittin are known to stimulate Gi activities. Here, we found melittin inhibited guanine nucleotide-dependent adenylyl cyclase activity in synaptic membranes of the rat cerebral cortex. However, in insect cell membranes overexpressing specific heterotrimeric G proteins using baculovirus expression system, melittin showed unique effects different from those by mastoparan on G protein activities. This peptide markedly stimulated Gi1 and G11 activities, whereas it did inhibit Gs activities. Kinetic studies revealed that the inhibition of Gs activity by melittin is attributed to the inhibition of GDP release in exchange for added guanine nucleotides (or the association of guanine nucleotides). Thus, melittin may be the first metabostatic peptide inhibiting G protein (Gs) activity, and both mechanisms through the stimulation of Gi and inhibition of Gs might be involved in the melittin-induced inhibition of adenylyl cyclase.

Damage to mitochondrial respiration chain is related to phospholipase A2 activation caused by tumor necrosis factor.

Tumor necrosis factor (TNF) has been shown to be cytotoxic to tumor cell lines in vitro, but the mechanism by which TNF exerts its cell growth-regulatory effects is not known. In this report, we used various inhibitors to investigate the sequence of events that lead to cytotoxic effects of TNF on L.P3 cells, a highly sensitive, murine fibroblast cell line. Our results indicate that mitochondrial respiration chains are damaged by a hydroxyl radical at an early stage of the cell lysis after TNF treatment. This event is followed by the activation of phospholipase A2, and finally leads to cell lysis.