Charge delocalisation and the design of novel mastoparan analogues: enhanced cytotoxicity and secretory efficacy of [Lys5, Lys8, Aib10]MP

Structure-Activity Relationship of New Chimeric Analogs of Mastoparan from the Wasp Venom Paravespula lewisii

Mastoparan (MP) is an antimicrobial cationic tetradecapeptide with the primary structure INLKALAALAKKIL-NH₂. This amphiphilic α-helical peptide was originally isolated from the venom of the wasp Paravespula lewisii. MP shows a variety of biological activities, such as inhibition of the growth of Gram-positive and Gram-negative bacteria, as well as hemolytic activity and activation of mast cell degranulation. Although MP appears to be toxic, studies have shown that its analogs have a potential therapeutic application as antimicrobial, antiviral and antitumor agents. In the present study we have designed and synthesized several new chimeric mastoparan analogs composed of MP and other biologically active peptides such as galanin, RNA III inhibiting peptide (RIP) or carrying benzimidazole derivatives attached to the ε-amino side group of Lys residue. Next, we compared their antimicrobial activity against three reference bacterial strains and conformational changes induced by membrane-mimic environments using circular dichroism (CD) spectroscopy. A comparative analysis of the relationship between the activity of peptides and the structure, as well as the calculated physicochemical parameters was also carried out. As a result of our structure-activity study, we have found two analogs of MP, MP-RIP and RIP-MP, with interesting properties. These two analogs exhibited a relatively high antibacterial activity against S. aureus compared to the other MP analogs, making them a potentially attractive target for further studies. Moreover, a comparative analysis of the relationship between peptide activity and structure, as well as the calculated physicochemical parameters, may provide information that may be useful in the design of new MP analogs.

Sweet as honey, bitter as bile: Mitochondriotoxic peptides and other therapeutic proteins isolated from animal tissues, for dealing with mitochondrial apoptosis

Mitochondria are subcellular organelles involved in cell metabolism and cell life-cycle. Their role in apoptosis regulation makes them an interesting target of new drugs for dealing with cancer or rare diseases. Several peptides and proteins isolated from animal and plant sources are known for their therapeutic properties and have been tested on cancer cell-lines and xenograft murine models, highlighting their ability in inducing cell-death by triggering mitochondrial apoptosis. Some of those molecules have been even approved as drugs. Conversely, many other bioactive compounds are still under investigation for their proapoptotic properties. In this review we report about a group of peptides, isolated from animal venoms, with potential therapeutic properties related to their ability in triggering mitochondrial apoptosis. This class of compounds is known with different names, such as mitochondriotoxins or mitocans.

A membrane disrupting toxin from wasp venom underlies the molecular mechanism of tissue damage

The molecular mechanism of the local hypersensitivity reactions to wasp venom including dermal necrosis remains an enigma regardless of the numerosity of the reported cases. In this study, we discovered a new membrane disrupting toxin, VESCP-M2 responsible for tissue damage symptoms following Vespa mandarinia envenomation. Electrophysiological assays revealed a potent ability of VESCP-M2 to permeate the cell membrane whereas in vivo experiments demonstrated that VESCP-M2 induces edema, pain and dermal necrosis characterized by the presence of morphological and behavioral phenotypes, pro-inflammatory mediators, biomarkers as well as the disruption of dermal tissue. This study presents the molecular mechanism and symptom-related function of VESCP-M2 which may form a basis for prognosis as well as therapeutic interventions.

The cationic tetradecapeptide mastoparan as a privileged structure for drug discovery: Enhanced antimicrobial properties of mitoparan analogues modified at position-14

Mastoparan (MP) peptides, distributed in insect venoms, induce a local inflammatory response post envenomation. Most endogenous MPs share common structural elements within a tetradecapeptide sequence that adopts an amphipathic helix whilst traversing biological membranes and when bound to an intracellular protein target. Rational modifications to increase cationic charge density and amphipathic helicity engineered mitoparan (MitP), a mitochondriotoxic bioportide and potent secretagogue. Following intracellular translocation, MitP is accreted by mitochondria thus indicating additional utility as an antimicrobial agent. Hence, the objectives of this study were to compare the antimicrobial activities of a structurally diverse set of cationic cell penetrating peptides, including both MP and MitP sequences, and to chemically engineer analogues of MitP for potential therapeutic applications. Herein, we confirm that, like MP, MitP is a privileged structure for the development of antimicrobial peptides active against both prokaryotic and eukaryotic pathogens. Collectively, MitP and target-selective chimeric analogues are broad spectrum antibiotics, with the Gram-negative A. baumannii demonstrating particular susceptibility. Modifications of MitP by amino acid substitution at position-14 produced peptides, Δ14MitP analogues, with unique pharmacodynamic properties. One example, [Ser¹⁴]MitP, lacks both cytotoxicity against human cell lines and mast cell secretory activity yet retains selective activity against the encapsulated yeast C. neoformans.

Differential Properties of Venom Peptides and Proteins in Solitary vs. Social Hunting Wasps

The primary functions of venoms from solitary and social wasps are different. Whereas most solitary wasps sting their prey to paralyze and preserve it, without killing, as the provisions for their progeny, social wasps usually sting to defend their colonies from vertebrate predators. Such distinctive venom properties of solitary and social wasps suggest that the main venom components are likely to be different depending on the wasps' sociality. The present paper reviews venom components and properties of the Aculeata hunting wasps, with a particular emphasis on the comparative aspects of venom compositions and properties between solitary and social wasps. Common components in both solitary and social wasp venoms include hyaluronidase, phospholipase A2, metalloendopeptidase, etc. Although it has been expected that more diverse bioactive components with the functions of prey inactivation and physiology manipulation are present in solitary wasps, available studies on venom compositions of solitary wasps are simply too scarce to generalize this notion. Nevertheless, some neurotoxic peptides (e.g., pompilidotoxin and dendrotoxin-like peptide) and proteins (e.g., insulin-like peptide binding protein) appear to be specific to solitary wasp venom. In contrast, several proteins, such as venom allergen 5 protein, venom acid phosphatase, and various phospholipases, appear to be relatively more specific to social wasp venom. Finally, putative functions of main venom components and their application are also discussed.

Strategies to stabilize cell penetrating peptides for in vivo applications

In the era of biomedicines and engineered carrier systems, cell penetrating peptides (CPPs) have been established as a promising tool for therapeutic application. Likewise, other therapeutic peptides, successful in vivo application of CPPs will strongly depend on peptide stability, the bottleneck for this type of biodegradable molecules. In this review, the authors describe the current knowledge of the in vivo degradation for known CPPs and the different strategies available to provide a higher resistance to metabolic degradation while preserving cell penetration efficiency. Peptide stability can be improved by different means, either modifying the structure to make it unrecognizable to proteases, or preventing access of proteolytic enzymes by applying conformation restriction or shielding strategies.

Antimicrobial activities and action mechanism studies of transportan 10 and its analogues against multidrug-resistant bacteria

The increased emergence of multidrug-resistant bacteria is perceived as a critical public health threat, creating an urgent need for the development of novel classes of antimicrobials. Cell-penetrating peptides that share common features with antimicrobial peptides have been found to have antimicrobial activity and are currently being considered as potential alternatives to antibiotics. Transportan 10 is a chimeric cell-penetrating peptide that has been reported to transport biologically relevant cargoes into mammalian cells and cause damage to microbial membranes. In this study, we designed a series of TP10 analogues and studied their structure-activity relationships. We first evaluated the antimicrobial activities of these compounds against multidrug-resistant bacteria, which are responsible for most nosocomial infections. Our results showed that several of these compounds had potent antimicrobial and biofilm-inhibiting activities. We also measured the toxicity of these compounds, finding that Lys substitution could increase the antimicrobial activity but significantly enhanced the cytotoxicity. Pro introduction could reduce the cytotoxicity but disrupted the helical structure, resulting in a loss of activity. In the mechanistic studies, TP10 killed bacteria by membrane-active and DNA-binding activities. In conclusion, TP10 and its analogues could be developed into promising antibiotic candidates for the treatment of infections caused by multidrug-resistant bacteria.

Three valuable peptides from bee and wasp venoms for therapeutic and biotechnological use: melittin, apamin and mastoparan

While knowledge of the composition and mode of action of bee and wasp venoms dates back 50 years, the therapeutic value of these toxins remains relatively unexploded. The properties of these venoms are now being studied with the aim to design and develop new therapeutic drugs. Far from evaluating the extensive number of monographs, journals and books related to bee and wasp venoms and the therapeutic effect of these toxins in numerous diseases, the following review focuses on the three most characterized peptides, namely melittin, apamin, and mastoparan. Here, we update information related to these compounds from the perspective of applied science and discuss their potential therapeutic and biotechnological applications in biomedicine.

Cell penetrating peptide-mediated transport enables the regulated secretion of accumulated cargoes from mast cells

The in vivo utility of technologies employing cell penetrating peptides and bioportides may be compromised by the general capacity of polycationic peptides to activate mast cell secretion. Moreover, the same technologies could be exploited in a clinical setting either to directly modulate intrinsic exocytotic mechanisms or to load mast cells with bioactive cargoes. Comparative investigations identified two cell penetrating vectors, Tat and C105Y, which readily translocate into mast cells without inducing receptor-independent exocytosis. Efficient Tat transduction also enabled the intracellular delivery and accumulation of cargoes within discrete intracellular compartments. A tetramethylrhodamine-Tat conjugate is effectively translocated into the secretory lysosomes of RBL-2H3 cells. In contract, the intracellular delivery of avidin, as a non-covalent complex with a biotinylated Tat vector, is also efficient but the protein is predominantly accumulated outside of secretory lysosomes. Significantly, both cargoes can be subsequently released following mast cell stimulation either by mastoparan, a wasp venom secretagogue, or by the physiological mechanism of antigen-induced aggregation of high affinity IgE receptors. These studies indicate that mast cells could be exploited to direct the delivery of bioactive agents to disease sites as an innovative cell-mediated therapy.

A mastoparan-derived peptide has broad-spectrum antiviral activity against enveloped viruses

Broad-spectrum antiviral drugs are urgently needed to treat individuals infected with new and re-emerging viruses, or with viruses that have developed resistance to antiviral therapies. Mammalian natural host defense peptides (mNHP) are short, usually cationic, peptides that have direct antimicrobial activity, and which in some instances activate cell-mediated antiviral immune responses. Although mNHP have potent activity in vitro, efficacy trials in vivo of exogenously provided mNHP have been largely disappointing, and no mNHP are currently licensed for human use. Mastoparan is an invertebrate host defense peptide that penetrates lipid bilayers, and we reasoned that a mastoparan analog might interact with the lipid component of virus membranes and thereby reduce infectivity of enveloped viruses. Our objective was to determine whether mastoparan-derived peptide MP7-NH2 could inactivate viruses of multiple types, and whether it could stimulate cell-mediated antiviral activity. We found that MP7-NH2 potently inactivated a range of enveloped viruses. Consistent with our proposed mechanism of action, MP7-NH2 was not efficacious against a non-enveloped virus. Pre-treatment of cells with MP7-NH2 did not reduce the amount of virus recovered after infection, which suggested that the primary mechanism of action in vitro was direct inactivation of virus by MP7-NH2. These results demonstrate for the first time that a mastoparan derivative has broad-spectrum antiviral activity in vitro and suggest that further investigation of the antiviral properties of mastoparan peptides in vivo is warranted.

Evaluating antioxidative activities of amino acid substitutions on mastoparan-B

Mastoparan-B is a peptide toxin isolated from the venom of Vespa basalis, the most dangerous hornet found in Taiwan. This study is aimed to evaluate the antioxidative activities of several amino acid substitutions on MP-B, and examined the influences of mast cell degranulation and hemolytic activities in parallel with antioxidative activities. The correlations between the biological function and amino acid sequence were assessed. Our study shows original MP-B is a valuable antioxidant at low concentration in competing with nitric-oxide for oxygen molecules and possesses good antioxidative enzyme activities resembled to superoxidase dismutase and glutathione peroxidase. And there are no predominant rates of mast cell degranulation and hemolytic effects in such condition. With proper substitutions, the reducing power, DPPH scavenging activity and glutathione reductase-like enzyme activity of MP-B can increase clearly. The results demonstrate that MP-B analogs are very potential to be applicable antioxidants for other antioxidative usages.

Cellular uptake of transportan 10 and its analogs in live cells: Selectivity and structure-activity relationship studies

Transportan 10 (TP10) is an amphipathic cell-penetrating peptide with high translocation ability. In order to obtain more details of structure-activity relationship of TP10, we evaluated the effects of structure and charge on its translocation ability. Our results demonstrated that disrupting the helical structure or Arg substitution could remarkably decrease the cellular uptake of TP10. However, increasing the number of positive charge was an effective strategy to enhance translocation ability of TP10. Furthermore, the molecular dynamics simulation supported the results derived from experiments, suggesting that higher membrane disturbance leads to higher cellular uptake of peptides. In addition, our study also demonstrated TP10 and its analogs preferentially entered cancer cells rather than normal cells. The uptake selectivity toward cancer cells makes TP10 and its analogs as potent CPPs for drug delivery.

Mitoparan and target-selective chimeric analogues: membrane translocation and intracellular redistribution induces mitochondrial apoptosis

Mastoparan, and structurally-related amphipathic peptides, may induce cell death by augmentation of necrotic and/or apoptotic pathways. To more precisely delineate cytotoxic mechanisms, we determined that [Lys(5,8)Aib(10)]mastoparan (mitoparan) specifically induces apoptosis of U373MG and ECV304 cells, as demonstrated by endonuclease and caspase-3 activation and phosphatidylserine translocation. Live cell imaging confirmed that, following translocation of the plasma membrane, mitoparan specifically co-localizes with mitochondria. Complementary studies indicated that mitoparan induces swelling and permeabilization of isolated mitochondria, through cooperation with a protein of the permeability transition pore complex VDAC, leading to the release of the apoptogenic factor, cytochrome c. N-terminal acylation of mitoparan facilitated the synthesis of chimeric peptides that incorporated target-specific address motifs including an integrin-specific RGD sequence and a Fas ligand mimetic. Significantly, these sychnologically-organised peptides demonstrated further enhanced cytotoxic potencies. We conclude that the cell penetrant, mitochondriotoxic and apoptogenic properties of mitoparan, and its chimeric analogues, offer new insights to the study and therapeutic induction of apoptosis.

Mastoparan inhibits beta-adrenoceptor-G(s) signaling by changing the localization of Galpha(s) in lipid rafts

Mastoparan, a wasp venom toxin, has various pharmacological activities, the mechanisms of which are still unknown. To clarify the action of mastoparan on G protein-coupled receptor-mediated signaling, we previously examined the effect of mastoparan on G(q)-mediated signaling and demonstrated that mastoparan binds to gangliosides causing a decrease in Galpha(q/11) content in lipid rafts, and resulting in the inhibition of G(q)-mediated phosphoinositide hydrolysis (Sugama et al., Mol. Pharmacol., 68, 1466, 2005). In the present study, we examined the effect of mastoparan on beta-adrenoceptor-G(s) signaling in 1321N1 human astrocytoma cells. Mastoparan inhibited isoproterenol-induced elevation of cyclic AMP in a concentration-dependent manner. Although mastoparan is known to be an activator of G(i), pertussis toxin only slightly attenuated mastoparan-induced inhibition of cyclic AMP elevation, suggesting that a major part of the inhibition of cyclic AMP elevation induced by mastoparan is not mediated by Galpha(i). By contrast, mastoparan-induced inhibition of cyclic AMP elevation was clearly attenuated by preincubation of the cells with ganglioside mixtures. Moreover, mastoparan changed the localization of Galpha(s) in lipid rafts without disrupting the structure of lipid rafts. Fluorescent staining analysis showed that mastoparan released GFP-Galpha(s) from plasma membranes into the cytosol. These results suggest that the mastoparan-induced suppression of cyclic AMP elevation is mainly caused by changing the localization of Galpha(s) in lipid rafts into a compartment in the cellular interior where it is not available to activate adenylyl cyclase.

Intracellular translocation of the decapeptide carboxyl terminal of Gi3 alpha induces the dual phosphorylation of p42/p44 MAP kinases

The carboxyl terminal of heterotrimeric G protein alpha subunits binds both G protein-coupled receptors and mastoparan (MP), a tetradecapeptide allostere. Moreover, peptides corresponding to the carboxyl domains of G(i)3alpha and G(t) display intrinsic biological activities in cell-free systems. Thus, the purpose of this study was to develop a cell penetrant delivery system to further investigate the biological properties of a peptide mimetic of the G(i)3alpha carboxyl terminal (G(i)3alpha(346-355); H-KNNLKECGLY-NH2). Kinetic studies, using a CFDA-conjugated analogue of G(i)3alpha(346-355), confirmed the rapid and efficient intracellular translocation of TP10-G(i)3alpha(346-355) (t(0.5) = 3 min). Translocated G(i)3alpha(346-355), but not other bioactive cargoes derived from PKC and the CB1 cannabinoid receptor, promoted the dual phosphorylation of p42/p44 MAPK without adverse changes in cellular viability. The relative specificity of this novel biological activity was further confirmed by the observation that translocated G(i)3alpha(346-355) did not influence the exocytosis of beta-hexoseaminidase from RBL-2H3, a secretory event stimulated by other cell penetrant peptide cargoes and MP. We conclude that TP10-G(i)3alpha(346-355) is a valuable, non-toxic research tool with which to study and modulate signal transduction pathways mediated by heterotrimeric G proteins and MAPK.

Mastoparan changes the cellular localization of Galphaq/11 and Gbeta through its binding to ganglioside in lipid rafts

Although it is known that mastoparan, a wasp venom toxin, directly activates Gi/o, mastoparan-induced biological responses are not always explained by this mechanism. For instance, we have demonstrated previously that mastoparan suppressed phosphoinositide hydrolysis induced by carbachol in human astrocytoma cells (FEBS Lett 206:91-94, 1990). In the present study, we examined whether mastoparan affected phosphoinositide hydrolysis by interacting with lipid rafts in PC-12 cells. Mastoparan inhibited UTP-induced increase in [Ca2+]i and phosphoinositide hydrolysis in a concentration-dependent manner. UTP-induced phosphoinositide hydrolysis occurred in lipid rafts, because methyl-beta-cyclodextrin, a disrupting regent of lipid rafts, inhibited the hydrolysis. Mastoparan changed the localization of Galphaq/11 and Gbeta together with cholesterol from lipid rafts to nonraft fractions or cytosol. These changes were inhibited by ganglioside mixtures, suggesting that mastoparan interacts with gangliosides in lipid rafts. In fact, ganglioside mixtures and neuraminidase, but not sialic acid, attenuated the inhibitory effect of mastoparan on phosphoinositide hydrolysis. Furthermore, fluorescence intensity of tyrosine residue of [Tyr3]mastoparan was potentiated by ganglioside mixtures, suggesting the direct binding of mastoparan to gangliosides. Mastoparan caused cytotoxicity of PC-12 cells in a concentration-dependent manner, determined by LDH release. The mastoparan-induced cytotoxicity was significantly inhibited by neuraminidase or gangliosides. The order of inhibitory potency of gangliosides was GT1b approximately GD1b > GD1a > GM1 >> GQ1b, but asialo-GM1 and sialic acid were inactive. These results suggest that mastoparan initially binds to gangliosides in lipid rafts and then it inhibits phosphoinositide hydrolysis by changing the localization of Galphaq/11 and Gbeta in lipid rafts.