Profiling the Linear Peptides of Venom from the Brazilian Scorpion Tityus serrulatus: Structural and Functional Characterization.

Scorpion venoms are a rich source of bioactive peptides, most of which are neurotoxic, with 30 to 70 amino acid residues in their sequences. There are a scarcity of reports in the literature concerning the short linear peptides found in scorpion venoms. This type of peptide toxin may be selectively extracted from the venom using 50% (v/v) acetonitrile. The use of LC-MS and MS/MS enabled the detection of 12 bioactive short linear peptides, of which six were identified as cryptides. These peptides were shown to be multifunctional, causing hemolysis, mast cell degranulation and lysis, edema, pain, and anxiety, increasing the complexity of the envenomation mechanism. Apparently, the natural functions of these peptide toxins are to induce inflammation and discomfort in the victims of scorpion stings.

Cytotoxic Cyclotides from Anchietea pyrifolia, a South American Plant Species.

Cyclotides are mini-proteins with potent bioactivities and outstanding potential for agricultural and pharmaceutical applications. More than 450 different plant cyclotides have been isolated from six angiosperm families. In Brazil, studies involving this class of natural products are still scarce, despite its rich floristic diversity. Herein were investigated the cyclotides from Anchietea pyrifolia roots, a South American medicinal plant from the family Violaceae. Fourteen putative cyclotides were annotated by LC-MS. Among these, three new bracelet cyclotides, anpy A-C, and the known cycloviolacins O4 (cyO4) and O17 (cyO17) were sequenced through a combination of chemical and enzymatic reactions followed by MALDI-MS/MS analysis. Their cytotoxic activity was evaluated by a cytotoxicity assay against three human cancer cell lines (colorectal carcinoma cells: HCT 116 and HCT 116 TP53-/- and breast adenocarcinoma, MCF 7). For all assays, the IC50 values of isolated compounds ranged between 0.8 and 7.3 µM. CyO17 was the most potent cyclotide for the colorectal cancer cell lines (IC50, 0.8 and 1.2 µM). Furthermore, the hemolytic activity of anpy A and B, cyO4, and cyO17 was assessed, and the cycloviolacins were the least hemolytic (HD50 > 156 µM). This work sheds light on the cytotoxic effects of the anpy cyclotides against cancer cells. Moreover, this study expands the number of cyclotides obtained to date from Brazilian plant biodiversity and adds one more genus containing these molecules to the list of the Violaceae family.

The Specific Elongation Factor to Selenocysteine Incorporation in Escherichia coli: Unique tRNASec Recognition and its Interactions.

Several molecular mechanisms are involved in the genetic code interpretation during translation, as codon degeneration for the incorporation of rare amino acids. One mechanism that stands out is selenocysteine (Sec), which requires a specific biosynthesis and incorporation pathway. In Bacteria, the Sec biosynthesis pathway has unique features compared with the eukaryote pathway as Ser to Sec conversion mechanism is accomplished by a homodecameric enzyme (selenocysteine synthase, SelA) followed by the action of an elongation factor (SelB) responsible for delivering the mature Sec-tRNASec into the ribosome by the interaction with the Selenocysteine Insertion Sequence (SECIS). Besides this mechanism being already described, the sequential events for Sec-tRNASec and SECIS specific recognition remain unclear. In this study, we determined the order of events of the interactions between the proteins and RNAs involved in Sec incorporation. Dissociation constants between SelB and the native as well as unacylated-tRNASec variants demonstrated that the acceptor stem and variable arm are essential for SelB recognition. Moreover, our data support the sequence of molecular events where GTP-activated SelB strongly interacts with SelA.tRNASec. Subsequently, SelB.GTP.tRNASec recognizes the mRNA SECIS to deliver the tRNASec to the ribosome. SelB in complex with its specific RNAs were examined using Hydrogen/Deuterium exchange mapping that allowed the determination of the molecular envelopes and its secondary structural variations during the complex assembly. Our results demonstrate the ordering of events in Sec incorporation and contribute to the full comprehension of the tRNASec role in the Sec amino acid biosynthesis, as well as extending the knowledge of synthetic biology and the expansion of the genetic code.

The effect of acidic pH on the adsorption and lytic activity of the peptides Polybia-MP1 and its histidine-containing analog in anionic lipid membrane: a biophysical study by molecular dynamics and spectroscopy.

Antimicrobial peptides (AMPs) are part of the innate immune system of many species. AMPs are short sequences rich in charged and non-polar residues. They act on the lipid phase of the plasma membrane without requiring membrane receptors. Polybia-MP1 (MP1), extracted from a native wasp, is a broad-spectrum bactericide, an inhibitor of cancer cell proliferation being non-hemolytic and non-cytotoxic. MP1 mechanism of action and its adsorption mode is not yet completely known. Its adsorption to lipid bilayer and lytic activity is most likely dependent on the ionization state of its two acidic and three basic residues and consequently on the bulk pH. Here we investigated the effect of bulk acidic (pH 5.5) and neutral pH (7.4) solution on the adsorption, insertion, and lytic activity of MP1 and its analog H-MP1 to anionic (7POPC:3POPG) model membrane. H-MP1 is a synthetic analog of MP1 with lysines replaced by histidines. Bulk pH changes could modulate this peptide efficiency. The combination of different experimental techniques and molecular dynamics (MD) simulations showed that the adsorption, insertion, and lytic activity of H-MP1 are highly sensitive to bulk pH in opposition to MP1. The atomistic details, provided by MD simulations, showed peptides contact their N-termini to the bilayer before the insertion and then lay parallel to the bilayer. Their hydrophobic faces inserted into the acyl chain phase disturb the lipid-packing.

Comparing activity, toxicity and model membrane interactions of Jelleine-I and Trp/Arg analogs: analysis of peptide aggregation.

Increasing resistance in antibiotic and chemotherapeutic treatments has been pushing studies of design and evaluation of bioactive peptides. Designing relies on different approaches from minimalist sequences and endogenous peptides modifications to computational libraries. Evaluation relies on microbiological tests. Aiming a deeper understanding, we chose the octapeptide Jelleine-I (JI) for its selective and low toxicity profile, designed small modifications combining the substitutions of Phe by Trp and Lys/His by Arg and tested the antimicrobial and anticancer activity on melanoma cells. Biophysical methods identified environment-dependent modulation of aggregation, but critical aggregation concentrations of JI and analogs in buffer show that peptides start membrane interactions as monomers. The presence of model membranes increases or reduces the partial aggregation of peptides. Compared to JI, analog JIF2WR shows the lowest tendency to aggregation on bacterial model membranes. JI and analogs are lytic to model membranes. Their composition-dependent performance indicates preference for the higher charged anionic bilayers in line with their superior performance toward Staphylococcus aureus and Streptococcus pneumoniae. JIF2WR presented the higher partitioning, higher lytic activity and lower aggregated contents. Despite these increased membranolytic activities, JIF2WR exhibited comparable antimicrobial activity in relation to JI at the expenses of some loss in selectivity. We found that the substitution Phe/Trp (JIF2W) tends to decrease antimicrobial but to increase anticancer activity and aggregation on model membranes and the toxicity toward human cells. However, the concomitant substitution Lys/His by Arg (JIF2WR) modulates some of these tendencies, increasing both the antimicrobial and the anticancer activity while decreasing the aggregation tendency.

Antifungal Activity, Toxicity, and Membranolytic Action of a Mastoparan Analog Peptide.

Invasive fungal infections, such as cryptococcosis and paracoccidioidomycosis are associated with significant rates of morbidity and mortality. Cryptococcosis, caused by Cryptococcus neoformans, is distributed worldwide and has received much attention as a common complication in patients with HIV. Invasive fungal infections are usually treated with a combination of amphotericin B and azoles. In addition, 5-fluorocytosine (5-FC) is applied in cryptococcosis, specifically to treat central nervous system infection. However, host toxicity, high cost, emerging number of resistant strains, and difficulty in developing new selective antifungals pose challenges. The need for new antifungals has therefore prompted a screen for inhibitory peptides, which have multiple mechanisms of action. The honeycomb moth Galleria mellonella has been widely used as a model system for evaluating efficacy of antifungal agents. In this study, a peptide analog from the mastoparan class of wasps (MK58911) was tested against Cryptococcus spp. and Paracoccidioides spp. In addition, peptide toxicity tests on lung fibroblasts (MRC5) and glioblastoma cells (U87) were performed. Subsequent tests related to drug interaction and mechanism of action were also performed, and efficacy and toxicity of the peptide were evaluated in vivo using the G. mellonella model. Our results reveal promising activity of the peptide, with an MIC in the range of 7.8-31.2 µg/mL, and low toxicity in MRC and U87 cells (IC50 > 500 µg/mL). Taken together, these results demonstrate that MK58911 is highly toxic in fungal cells, but not mammalian cells (SI > 16). The mechanism of toxicity involved disruption of the plasma membrane, leading to death of the fungus mainly by necrosis. In addition, no interaction with the drugs amphotericin B and fluconazole was found either in vitro or in vivo. Finally, the peptide showed no toxic effects on G. mellonella, and significantly enhanced survival rates of larvae infected with C. neoformans. Although not statistically significant, treatment of larvae with all doses of MK58911 showed a similar trend in decreasing the fungal burden of larvae. These effects were independent of any immunomodulatory activity. Overall, these results present a peptide with potential for use as a new antifungal drug to treat systemic mycoses.

Profiling the short, linear, non-disulfide bond-containing peptidome from the venom of the scorpion Tityus obscurus.

Many scorpion accidents occur in the Brazilian Amazonian region and are frequently caused by Tityus obscurus. Approximately 5% of the crude venom of this species is composed of short linear, non-disulfide-bridged peptides, which have not been intensively investigated. As a consequence, only a few of these peptides have been structurally and functionally characterized to date. In the present paper, the peptide fraction of the venom was subjected to peptide profiling using an LCMS-IT-TOF/MS and MSn system. The analysis detected 320 non-disulfide bond-containing peptides (NDBPs), of which twenty-seven had their sequences assigned; among them, thirteen peptides were characterized, constituting novel toxins in T. obscurus venom. Some of the novel peptides showed similarities to hypotensin-like toxins, while other peptides appear to be natural fragments of neurotoxins. The novel peptides were submitted to a series of bioassays, revealing that many are multifunctional toxins that cause, for example, pain, edema formation and hemolysis to potentiate strong inflammatory processes and alterations in the locomotion and lifting activities in the victims of stinging. Knowledge of the complex matrix of peptides composing the venom of T. obscurus will contribute to better understanding of the complex mechanism of envenoming caused by stinging accidents. SIGNIFICANCE: The scorpion Tityus obscurus causes many envenoming accidents of medical importance in Brazilian Amazon region; despite to this, very few is known about the toxinology of this animal. The knowledge about the venom composition and mechanisms of action is very important to understand the physiopathology processes related to the envenoming caused by this animal. The proteopeptidomic investigations of scorpion venoms in general have focused mainly the neurotoxins (which are disulfide bonds containing peptides) and large proteins. The short, linear, non-disulfide bonds containing peptides (NDBPs) represent up to 5% of scorpion venom compositions; however, they have been few investigated in comparison with the neurotoxins. The present study used a mass spectrometric approach to detect 320 NDBPs and to sequence 27 of them; pharmacological assays permitted to characterize 13 NDBPs as novel toxins involved with inflammation, pain and edema formation.

Profiling the short, linear, non-disulfide bond-containing peptidome from the venom of the scorpion Tityus obscurus

Many scorpion accidents occur in the Brazilian Amazonian region and are frequently caused by Tityus obscurus. Approximately 5% of the crude venom of this species is composed of short linear, non-disulfide-bridged peptides, which have not been intensively investigated. As a consequence, only a few of these peptides have been structurally and functionally characterized to date. In the present paper, the peptide fraction of the venom was subjected to peptide profiling using an LCMS-IT-TOF/MS and MSn system. The analysis detected 320 non-disulfide bond-containing peptides (NDBPs), of which twenty-seven had their sequences assigned; among them, thirteen peptides were characterized, constituting novel toxins in T. obscurus venom. Some of the novel peptides showed similarities to hypotensin-like toxins, while other peptides appear to be natural fragments of neurotoxins. The novel peptides were submitted to a series of bioassays, revealing that many are multifunctional toxins that cause, for example, pain, edema formation and hemolysis to potentiate strong inflammatory processes and alterations in the locomotion and lifting activities in the victims of stinging. Knowledge of the complex matrix of peptides composing the venom of T. obscurus will contribute to better understanding of the complex mechanism of envenoming caused by stinging accidents. Significance: The scorpion Tityus obscurus causes many envenoming accidents of medical importance in Brazilian Amazon region; despite to this, very few is known about the toxinology of this animal. The knowledge about the venom composition and mechanisms of action is very important to understand the physiopathology processes related to the envenoming caused by this animal. The proteopeptidomic investigations of scorpion venoms in general have focused mainly the neurotoxins (which are disulfide bonds containing peptides) and large proteins. The short, linear, non-disulfide bonds containing peptides (NDBPs) represent up to 5% of scorpion venom compositions; however, they have been few investigated in comparison with the neurotoxins. The present study used a mass spectrometric approach to detect 320 NDBPs and to sequence 27 of them; pharmacological assays permitted to characterize 13 NDBPs as novel toxins involved with inflammation, pain and edema formation.

Profiling the short, linear, non-disulfide bond-containing peptidome from the venom of the scorpion Tityus obscurus

Many scorpion accidents occur in the Brazilian Amazonian region and are frequently caused by Tityus obscurus. Approximately 5% of the crude venom of this species is composed of short linear, non-disulfide-bridged peptides, which have not been intensively investigated. As a consequence, only a few of these peptides have been structurally and functionally characterized to date. In the present paper, the peptide fraction of the venom was subjected to peptide profiling using an LCMS-IT-TOF/MS and MSn system. The analysis detected 320 non-disulfide bond-containing peptides (NDBPs), of which twenty-seven had their sequences assigned; among them, thirteen peptides were characterized, constituting novel toxins in T. obscurus venom. Some of the novel peptides showed similarities to hypotensin-like toxins, while other peptides appear to be natural fragments of neurotoxins. The novel peptides were submitted to a series of bioassays, revealing that many are multifunctional toxins that cause, for example, pain, edema formation and hemolysis to potentiate strong inflammatory processes and alterations in the locomotion and lifting activities in the victims of stinging. Knowledge of the complex matrix of peptides composing the venom of T. obscurus will contribute to better understanding of the complex mechanism of envenoming caused by stinging accidents. Significance: The scorpion Tityus obscurus causes many envenoming accidents of medical importance in Brazilian Amazon region; despite to this, very few is known about the toxinology of this animal. The knowledge about the venom composition and mechanisms of action is very important to understand the physiopathology processes related to the envenoming caused by this animal. The proteopeptidomic investigations of scorpion venoms in general have focused mainly the neurotoxins (which are disulfide bonds containing peptides) and large proteins. The short, linear, non-disulfide bonds containing peptides (NDBPs) represent up to 5% of scorpion venom compositions; however, they have been few investigated in comparison with the neurotoxins. The present study used a mass spectrometric approach to detect 320 NDBPs and to sequence 27 of them; pharmacological assays permitted to characterize 13 NDBPs as novel toxins involved with inflammation, pain and edema formation.

Trypanocidal activity of mastoparan from Polybia paulista wasp venom by interaction with TcGAPDH.

Chagas disease, considered a neglected disease, is a parasitic infection caused by Trypanosoma cruzi, which is endemic throughout the world. Previously, the antimicrobial effect of Mastoparan (MP) from Polybia paulista wasp venom against bacteria was described. To continue the study, we report in this short communication the antimicrobial effect of MP against Trypanosoma cruzi. MP inhibits all T. cruzi developmental forms through the inhibition of TcGAPDH suggested by the molecular docking. In conclusion, we suggest there is an antimicrobial effect also on T. cruzi.

Paulistine--The Functional Duality of a Wasp Venom Peptide Toxin.

It has been reported that Paulistine in the venom of the wasp Polybia paulista co-exists as two different forms: an oxidized form presenting a compact structure due to the presence of a disulfide bridge, which causes inflammation through an apparent interaction with receptors in the 5-lipoxygenase pathway, and a naturally reduced form (without the disulfide bridge) that exists in a linear conformation and which also causes hyperalgesia and acts in the cyclooxygenase type II pathway. The reduced peptide was acetamidomethylated (Acm-Paulistine) to stabilize this form, and it still maintained its typical inflammatory activity. Oxidized Paulistine docks onto PGHS2 (COX-2) molecules, blocking the access of oxygen to the heme group and inhibiting the inflammatory activity of Acm-Paulistine in the cyclooxygenase type II pathway. Docking simulations revealed that the site of the docking of Paulistine within the PGHS2 molecule is unusual among commercial inhibitors of the enzyme, with an affinity potentially much higher than those observed for traditional anti-inflammatory drugs. Therefore, Paulistine causes inflammatory activity at the level of the 5-lipooxygenase pathway and, in parallel, it competes with its reduced form in relation to the activation of the cyclooxygenase pathway. Thus, while the reduced Paulistine causes inflammation, its oxidized form is a potent inhibitor of this activity.

Peptidome profiling of venom from the social wasp Polybia paulista.

Most crude venom from Polybia paulista is composed of short, linear peptides; however, only five of these peptides are structurally and functionally characterized. Therefore, the peptides in this venom were profiled using an HPLC-IT-TOF/MS and MS(n) system. The presence of type -d and -w ions that are generated from the fragmentation of the side chains was used to resolve I/L ambiguity. The distinction between K and Q residues was achieved through esterification of the α- and ε-amino groups in the peptide chains, followed by mass spectrometry analysis. Fourteen major peptides were detected in P. paulista venom and sequenced; all the peptides were synthesized on solid-phase and submitted to a series of bioassays. Five of them had been previously characterized, and nine were novel toxins. The novel peptides correspond to two wasp kinins, two chemotactic components, three mastoparans, and two peptides of unknown function. The seven novel peptides with identified functions appear to act synergistically with the previously known ones, constituting three well-known families of peptide toxins (wasp kinins, chemotactic peptides, and mastoparans) in the venom of social wasps. These multifunctional toxins can cause pain, oedema formation, haemolysis, chemotaxis of PMNLs, and mast cell degranulation in victims who are stung by wasps.

Effect of the aspartic acid D2 on the affinity of Polybia-MP1 to anionic lipid vesicles.

Polybia-MP1 (IDWKKLLDAAKQIL-NH2), a helical peptide extracted from the venom of a Brazilian wasp, has broad-spectrum antimicrobial activities without being hemolytic or cytotoxic. This peptide has also displayed anticancer activity against cancer cell cultures. Despite its high selectivity, MP1 has an unusual low net charge (Q = +2). The aspartic residue (D2) in the N-terminal region plays an important role in its affinity and selectivity; its substitution by asparagine (D2N mutant) led to a less selective peptide. Aiming to explore the importance of this residue for the peptides' affinity, we compared the zwitterionic and anionic vesicle adsorption activity of Polybia-MP1 versus its D2N mutant and also mastoparan X (MPX). The adsorption, electrostatic, and conformational free energies were assessed by circular dichroism (CD) and fluorescence titrations using large unilamellar vesicles (LUVs) at the same conditions in association with measurement of the zeta potential of LUVs in the presence of the peptides. The adsorption free energies of the peptides, determined from the partition coefficients, indicated higher affinity of MP1 to anionic vesicles compared with the D2N mutant and MPX. The electrostatic and conformational free energies of MP1 in anionic vesicles are less favorable than those found for the D2N mutant and MPX. Therefore, the highest affinity of MP1 to anionic vesicles is likely due to other energetic contributions. The presence of D2 in MP1 makes these energetic components 1.2 and 1.5 kcal/mol more favorable compared with the D2N mutant and MPX, respectively.

Structure-function relationships of the peptide Paulistine: a novel toxin from the venom of the social wasp Polybia paulista.

BACKGROUND: The peptide Paulistine was isolated from the venom of wasp Polybia paulista. This peptide exists under a natural equilibrium between the forms: oxidised - with an intra-molecular disulphide bridge; and reduced - in which the thiol groups of the cysteine residues do not form the disulphide bridge. The biological activities of both forms of the peptide are unknown up to now. METHODS: Both forms of Paulistine were synthesised and the thiol groups of the reduced form were protected with the acetamidemethyl group [Acm-Paulistine] to prevent re-oxidation. The structure/activity relationships of the two forms were investigated, taking into account the importance of the disulphide bridge. RESULTS: Paulistine has a more compact structure, while Acm-Paulistine has a more expanded conformation. Bioassays reported that Paulistine caused hyperalgesia by interacting with the receptors of lipid mediators involved in the cyclooxygenase type II pathway, while Acm-Paullistine also caused hyperalgesia, but mediated by receptors involved in the participation of prostanoids in the cyclooxygenase type II pathway. CONCLUSION: The acetamidemethylation of the thiol groups of cysteine residues caused small structural changes, which in turn may have affected some physicochemical properties of the Paulistine. Thus, the dissociation of the hyperalgesy from the edematogenic effect when the actions of Paulistine and Acm-Paulistine are compared to each other may be resulting from the influence of the introduction of Acm-group in the structure of Paulistine. GENERAL SIGNIFICANCE: The peptides Paulistine and Acm-Paulistine may be used as interesting tools to investigate the mechanisms of pain and inflammation in future studies.

Peptide diversity in the venom of the social wasp Polybia paulista (Hymenoptera): a comparison of the intra- and inter-colony compositions.

The venoms of the social wasps evolved to be used as defensive tools to protect the colonies of these insects against the attacks of predators. Previous studies estimated the presence of a dozen peptide components in the venoms of each species of these insects, which altogether comprise up to 70% of the weight of freeze-dried venoms. In the present study, an optimized experimental protocol is reported that utilizes liquid chromatography coupled to electrospray ionization mass spectrometry for the detection of peptides in the venom of the social wasp Polybia paulista; peptide profiles for both intra- and inter-colonial comparisons were obtained using this protocol. The results of our study revealed a surprisingly high level of intra- and inter-colonial variability for the same wasp species. We detected 78-108 different peptides in the venom of different colonies of P. paulista in the molar mass range from 400 to 3000Da; among those, only 36 and 44 common peptides were observed in the inter- and intra-colony comparisons, respectively.

Influence of the bilayer composition on the binding and membrane disrupting effect of Polybia-MP1, an antimicrobial mastoparan peptide with leukemic T-lymphocyte cell selectivity.

This study shows that MP-1, a peptide from the venom of the Polybia paulista wasp, is more toxic to human leukemic T-lymphocytes than to human primary lymphocytes. By using model membranes and electrophysiology measurements to investigate the molecular mechanisms underlying this selective action, the porelike activity of MP-1 was identified with several bilayer compositions. The highest average conductance was found in bilayers formed by phosphatidylcholine or a mixture of phosphatidylcholine and phosphatidylserine (70:30). The presence of cholesterol or cardiolipin substantially decreases the MP-1 pore activity, suggesting that the membrane fluidity influences the mechanism of selective toxicity. The determination of partition coefficients from the anisotropy of Trp indicated higher coefficients for the anionic bilayers. The partition coefficients were found to be 1 order of magnitude smaller when the bilayers contain cholesterol or a mixture of cholesterol and sphingomyelin. The blue shift fluorescence, anisotropy values, and Stern-Volmer constants are indications of a deeper penetration of MP-1 into anionic bilayers than into zwitterionic bilayers. Our results indicate that MP-1 prefers to target leukemic cell membranes, and its toxicity is probably related to the induction of necrosis and not to DNA fragmentation. This mode of action can be interpreted considering a number of bilayer properties like fluidity, lipid charge, and domain formation. Cholesterol-containing bilayers are less fluid and less charged and have a tendency to form domains. In comparison to healthy cells, leukemic T-lymphocyte membranes are deprived of this lipid, resulting in decreased peptide binding and lower conductance. We showed that the higher content of anionic lipids increases the level of binding of the peptide to bilayers. Additionally, the absence of cholesterol resulted in enhanced pore activity. These findings may drive the selective toxicity of MP-1 to Jurkat cells.

New insight into the mechanism of action of wasp mastoparan peptides: lytic activity and clustering observed with giant vesicles.

Antimicrobial peptides of the mastoparans family exert their bactericidal activity by binding to lipid membranes, inducing pores or defects and leaking the internal contents of vesicles and cells. However, this does not seem to be the only mechanism at play, and they might be important in the search for improved peptides with lower undesirable side effects. This work deals with three mastoparans peptides, Polybia-MP-1(MP-1), N2-Polybia-MP-1 (N-MP-1), and Mastoparan X (MPX), which exhibit high sequence homology. They all have three lysine residues and amidated C termini, but because of the presence of two, one, and no aspartic acid residues, respectively, they have +2, +3, and +4 net charges at physiological pH. Here we focus on the effects of these mastoparans peptides on anionic model membranes made of palmitoleyoilphosphatidylcholine (POPC) and palmitoleyoilphosphatidylglycerol (POPG) at 1:1 and 3:1 molar ratios in the presence and in the absence of saline buffer. Zeta potential experiments were carried out to measure the extent of the peptides' binding and accumulation at the vesicle surface, and CD spectra were acquired to quantify the helical structuring of the peptides upon binding. Giant unilamellar vesicles were observed under phase contrast and fluorescence microscopy. We found that the three peptides induced the leakage of GUVs at a gradual rate with many characteristics of the graded mode. This process was faster in the absence of saline buffer. Additionally, we observed that the peptides induced the formation of dense regions of phospholipids and peptides on the GUV surface. This phenomenon was easily observable for the more charged peptides (MPX > N-MP-1 > MP-1) and in the absence of added salt. Our data suggest that these mastoparans accumulate on the bilayer surface and induce a transient interruption to its barrier properties, leaking the vesicle contents. Next, the bilayer recovers its continuity, but this happens in an inhomogeneous way, forming a kind of ply with peptides sandwiched between two juxtaposed membranes. Eventually, a peptide-lipid aggregate forming a lump is formed at high peptide-to-lipid ratios.

The effect of acidic residues and amphipathicity on the lytic activities of mastoparan peptides studied by fluorescence and CD spectroscopy.

Some mastoparan peptides extracted from social wasps display antimicrobial activity and some are hemolytic and cytotoxic. Although the cell specificity of these peptides is complex and poorly understood, it is believed that their net charges and their hydrophobicity contribute to modulate their biological activities. We report a study, using fluorescence and circular dichroism spectroscopies, evaluating the influence of these two parameters on the lytic activities of five mastoparans in zwitterionic and anionic phospholipid vesicles. Four of these peptides, extracted from the venom of the social wasp Polybia paulista, present both acidic and basic residues with net charges ranging from +1 to +3 which were compared to Mastoparan-X with three basic residues and net charge +4. Previous studies revealed that these peptides have moderate-to-strong antibacterial activity against Gram-positive and Gram-negative microorganisms and some of them are hemolytic. Their affinity and lytic activity in zwitterionic vesicles decrease with the net electrical charges and the dose response curves are more cooperative for the less charged peptides. Higher charged peptides display higher affinity and lytic activity in anionic vesicles. The present study shows that the acidic residues play an important role in modulating the peptides' lytic and biological activities and influence differently when the peptide is hydrophobic or when the acidic residue is in a hydrophilic peptide.

Investigating the effect of different positioning of lysine residues along the peptide chain of mastoparans for their secondary structures and biological activities.

In order to investigate the effect of the different positions of the positive charges generated by the ionization of the side-chain of lysine residues, on the structure-activity relationship of the mastoparans, the peptides Protonectarina-MP (INWKALLDAAKKVL-NH2), Parapolybia-MP (INWKKMAATALKMI-NH2) and Asn-2-Polybia-MP I (INWKKLLDAAKQIL-NH2) and MK-578 (INWLKAKKVAGMIL-NH2) were investigated as models. Thus, the four peptides had their secondary structure studied and were submitted to assays of mast cell degranulation, hemolysis, and antibiosis. The results of the bioassays made clear that those peptides bearing the positive charges positioned at the positions 4/5 and/or from 11 to 13 are the most active ones; meanwhile, the localization of the positive charges in the middle of peptide chain resulted in a poorly active peptide. Thus, Protonectarina-MP, Parapolybia-MP, and Asn-2-Polybia-MP I presented physiologically important hemolysis and antibiosis, while MK-578 presented only a reduced antibiotic activity. Circular dichroism analysis were carried-out in different environments revealing that the anionic environment of a mixture of phosphatidylcholine and phosphatidylglycerol (70:30) liposomes favored the higher helical content of the four peptides in this study in relation to the zwiterionic environment of 100% phosphatidylcholine liposomes. The positioning of the lysine residues at the strategic positions (4/5 and 11-13), flanking and maintaining stable α-helix which extends from the 4th to the 13th residue along the peptide chain, seems to contribute to maximal lytic efficiency of the mastoparans, which in turn results in a more homogeneous hydrophobic surface in the amphipathic structure.

Profiling the proteome of the venom from the social wasp Polybia paulista: a clue to understand the envenoming mechanism.

The study reported here is a classical bottom-up proteomic approach where proteins from wasp venom were extracted and separated by 2-DE; the individual protein spots were proteolytically digested and subsequently identified by using tandem mass spectrometry and database query with the protein search engine MASCOT. Eighty-four venom proteins belonging to 12 different molecular functions were identified. These proteins were classified into three groups; the first is constituted of typical venom proteins: antigens-5, hyaluronidases, phospholipases, heat shock proteins, metalloproteinases, metalloproteinase-desintegrin like proteins, serine proteinases, proteinase inhibitors, vascular endothelial growth factor-related protein, arginine kinases, Sol i-II and -II like proteins, alpha-glucosidase, and superoxide dismutases. The second contained proteins structurally related to the muscles that involves the venom reservoir. The third group, associated with the housekeeping of cells from venom glands, was composed of enzymes, membrane proteins of different types, and transcriptional factors. The composition of P. paulista venom permits us to hypothesize about a general envenoming mechanism based on five actions: (i) diffusion of venom through the tissues and to the blood, (ii) tissue, (iii) hemolysis, (iv) inflammation, and (v) allergy-played by antigen-5, PLA1, hyaluronidase, HSP 60, HSP 90, and arginine kinases.