A short proregion of trialysin, a pore-forming protein of Triatoma infestans salivary glands, controls activity by folding the N-terminal lytic motif

Bacteriolytic activity in saliva of the hematophagous Triatoma infestans (Reduviidae) and novel characterization and expression site of a third lysozyme

Saliva of hematophagous insects contains many different compounds, mainly acting as anticoagulants. Investigating the bacteriolytic compounds of the saliva of the bloodsucking Triatoma infestans photometrically between pH 3 and pH 10 using unfed fifth instars and nymphs up to 15 days after feeding, we found bacteriolytic activity against lyophilized Micrococcus luteus was stronger at pH 4 and pH 6. After feeding, the activity level at pH 4 was unchanged, but at pH 6 more than doubled between 3 and 7 days after feeding. In zymographs of the saliva and after incubation at pH 4, bacteriolytic activity against Micrococcus luteus was present at eight lysis zones between 14.1 and 38.5 kDa, showing the strongest activity at 24.5 kDa. After incubation at pH 6, lysis zones only appeared at 15.3, 17, and 31.4 kDa. Comparing zymographs of the saliva of unfed and fed nymphs, bacteriolytic activity at 17 kDa increased after feeding. In total nine lysis bands appeared, also at >30 kDa, so far unreported in the saliva of triatomines. Reverse transcription polymerase chain reaction using oligonucleotides based on the previously described lysozyme gene of T. infestans, TiLys1, verified expression of genes encoding TiLys1 and TiLys2 in the salivary glands, but also of an undescribed third lysozyme, TiLys3, of which the cloned cDNA shares characteristics with other c-type lysozymes of insects. While TiLys1 was expressed in the tissue of all three salivary glands, transcripts of TiLys2 and of TiLys3 seem to be present only in the gland G1 and G3, respectively.

An Assassin's Secret: Multifunctional Cytotoxic Compounds in the Predation Venom of the Assassin Bug Psytalla horrida (Reduviidae, Hemiptera)

Predatory assassin bugs produce venomous saliva that enables them to overwhelm, kill, and pre-digest large prey animals. Venom from the posterior main gland (PMG) of the African assassin bug Psytalla horrida has strong cytotoxic effects, but the responsible compounds are yet unknown. Using cation-exchange chromatography, we fractionated PMG extracts from P. horrida and screened the fractions for toxicity. Two venom fractions strongly affected insect cell viability, bacterial growth, erythrocyte integrity, and intracellular calcium levels in Drosophila melanogaster olfactory sensory neurons. LC-MS/MS analysis revealed that both fractions contained gelsolin, redulysins, S1 family peptidases, and proteins from the uncharacterized venom protein family 2. Synthetic peptides representing the putative lytic domain of redulysins had strong antimicrobial activity against Escherichia coli and/or Bacillus subtilis but only weak toxicity towards insect or mammalian cells, indicating a primary role in preventing the intake of microbial pathogens. In contrast, a recombinant venom protein family 2 protein significantly reduced insect cell viability but exhibited no antibacterial or hemolytic activity, suggesting that it plays a role in prey overwhelming and killing. The results of our study show that P. horrida secretes multiple cytotoxic compounds targeting different organisms to facilitate predation and antimicrobial defense.

Alkylation converts riboflavin into an efficient photosensitizer of phospholipid membranes

A new decyl chain [-(CH₂)₉CH₃] riboflavin conjugate has been synthesized and investigated. A nucleophilic substitution (S_N2) reaction was used for coupling the alkyl chain to riboflavin (Rf), a model natural photosensitizer. As expected, the alkylated compound (decyl-Rf) is significantly more lipophilic than its precursor and efficiently intercalates within phospholipid bilayers, increasing its fluorescence quantum yield. The oxidative damage to lipid membranes photoinduced by decyl-Rf was investigated in large and giant unilamellar vesicles (LUVs and GUVs, respectively) composed of different phospholipids. Using a fluorogenic probe, fast radical formation and singlet oxygen generation was demonstrated upon UVA irradiation in vesicles containing decyl-Rf. Photosensitized formation of conjugated dienes and hydroperoxides, and membrane leakage in LUVs rich in poly-unsaturated fatty acids were also investigated. The overall assessment of the results shows that decyl-Rf is a significantly more efficient photosensitizer of lipids than its unsubstituted precursor and that the association to lipid membranes is key to trigger phospholipid oxidation. Alkylation of hydrophilic photosensitizers as a simple and general synthetic tool to obtain efficient photosensitizers of biomembranes, with potential applications, is discussed.

Effect of Triatoma infestans saliva on mouse immune system cells: The role of the pore-forming salivary protein trialysin

Triatoma infestans is one of the most important vectors of Trypanosoma cruzi in the Americas. While feeding, they release large amounts of saliva that will counteract the host's responses triggered at the bite site. Despite the various activities described on T. infestans saliva, little is known about its effect on the modulation of the host's immune system. This work aimed to describe the effects of T. infestans saliva on cells of the mouse immune system and access the role in hematophagy. The effect of saliva or salivary gland extract (SGE) was evaluated in vivo and in vitro by direct T. infestans feeding on mice or using different biological assays. Mice that were submitted to four bites by three specimens of T. infestans had their anti-saliva IgG serum levels approximately 2.4 times higher than controls, but no change in serum IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-γ, and TNF-α levels was observed. No macroscopic alterations were seen at the bite site, but an accumulation of mononuclear and polymorphonuclear cells shortly after the bite and 24 h later were observed in histological cuts. At low concentrations (up to ∼5 μg/well), SGE induced TNF-α production by macrophages and spleen cells, IFN-γ and IL-10 by spleen cells and NO by macrophages. However, at higher concentrations (10 and 20 μg/well), viability of macrophages and spleen cells was reduced by SGE, reducing the production of NO and cytokines (except TNF-α). The salivary trialysin was the main inducer of cell death as macrophage viability and NO production was restored in assays carried out with SGE from trialysin knockdown insects. The reduction of the salivary trialysin by RNAi affected the total ingestion rate, the weight gain, and retarded the molt from second to the fifth instar of T. infestans nymphs fed on mice. The results show that T. infestans saliva modulates the activity of cells of the host immune system and trialysin is an important salivary molecule that reduces host cells viability and impacts the feeding performance of T. infestans feeding on live hosts.

An Integrative Sialomic Analysis Reveals Molecules From Triatoma sordida (Hemiptera: Reduviidae)

Triatomines have evolved salivary glands that produce versatile molecules with various biological functions, including those leading their interactions with vertebrate hosts’ hemostatic and immunological systems. Here, using high-throughput transcriptomics and proteomics, we report the first sialome study on the synanthropic triatomine Triatoma sordida. As a result, 57,645,372 reads were assembled into 26,670 coding sequences (CDS). From these, a total of 16,683 were successfully annotated. The sialotranscriptomic profile shows Lipocalin as the most abundant protein family within putative secreted transcripts. Trialysins and Kazal-type protease inhibitors have high transcript levels followed by ubiquitous protein families and enzyme classes. Interestingly, abundant trialysin and Kazal-type members are highlighted in this triatomine sialotranscriptome. Furthermore, we identified 132 proteins in T. sordida salivary gland soluble extract through LC-MS/MS spectrometry. Lipocalins, Hemiptera specific families, CRISP/Antigen-5 and Kazal-type protein inhibitors proteins were identified. Our study provides a comprehensive description of the transcript and protein compositions of the salivary glands of T. sordida. It significantly enhances the information in the Triatominae sialome databanks reported so far, improving the understanding of the vector’s biology, the hematophagous behaviour, and the Triatominae subfamily’s evolution.

Correlating biological activity to thermo-structural analysis of the interaction of CTX with synthetic models of macrophage membranes

The important pharmacological actions of Crotoxin (CTX) on macrophages, the main toxin in the venom of Crotalus durissus terrificus, and its important participation in the control of different pathophysiological processes, have been demonstrated. The biological activities performed by macrophages are related to signaling mediated by receptors expressed on the membrane surface of these cells or opening and closing of ion channels, generation of membrane curvature and pore formation. In the present work, the interaction of the CTX complex with the cell membrane of macrophages is studied, both using biological cells and synthetic lipid membranes to monitor structural alterations induced by the protein. Here we show that CTX can penetrate THP-1 cells and induce pores only in anionic lipid model membranes, suggesting that a possible access pathway for CTX to the cell is via lipids with anionic polar heads. Considering that the selectivity of the lipid composition varies in different tissues and organs of the human body, the thermostructural studies presented here are extremely important to open new investigations on the biological activities of CTX in different biological systems.

Missiles of Mass Disruption: Composition and Glandular Origin of Venom Used as a Projectile Defensive Weapon by the Assassin Bug Platymeris rhadamanthus

Assassin bugs (Reduviidae) produce venoms that are insecticidal, and which induce pain in predators, but the composition and function of their individual venom components is poorly understood. We report findings on the venom system of the red-spotted assassin bug Platymeris rhadamanthus, a large species of African origin that is unique in propelling venom as a projectile weapon when threatened. We performed RNA sequencing experiments on venom glands (separate transcriptomes of the posterior main gland, PMG, and the anterior main gland, AMG), and proteomic experiments on venom that was either defensively propelled or collected from the proboscis in response to electrostimulation. We resolved a venom proteome comprising 166 polypeptides. Both defensively propelled venom and most venom samples collected in response to electrostimulation show a protein profile similar to the predicted secretory products of the PMG, with a smaller contribution from the AMG. Pooled venom samples induce calcium influx via membrane lysis when applied to mammalian neuronal cells, consistent with their ability to cause pain when propelled into the eyes or mucus membranes of potential predators. The same venom induces rapid paralysis and death when injected into fruit flies. These data suggest that the cytolytic, insecticidal venom used by reduviids to capture prey is also a highly effective defensive weapon when propelled at predators.

Parallel damage in mitochondria and lysosomes is an efficient way to photoinduce cell death

Cells challenged by photosensitized oxidations face strong redox stresses and rely on autophagy to either survive or die. However, the use of macroautophagy/autophagy to improve the efficiency of photosensitizers, in terms of inducing cell death, remains unexplored. Here, we addressed the concept that a parallel damage in the membranes of mitochondria and lysosomes leads to a scenario of autophagy malfunction that can greatly improve the efficiency of the photosensitizer to cause cell death. Specific damage to these organelles was induced by irradiation of cells pretreated with 2 phenothiazinium salts, methylene blue (MB) and 1,9-dimethyl methylene blue (DMMB). At a low concentration level (10 nM), only DMMB could induce mitochondrial damage, leading to mitophagy activation, which did not progress to completion because of the parallel damage in lysosome, triggering cell death. MB-induced photodamage was perceived almost instantaneously after irradiation, in response to a massive and nonspecific oxidative stress at a higher concentration range (2 µM). We showed that the parallel damage in mitochondria and lysosomes activates and inhibits mitophagy, leading to a late and more efficient cell death, offering significant advantage (2 orders of magnitude) over photosensitizers that cause unspecific oxidative stress. We are confident that this concept can be used to develop better light-activated drugs. Abbreviations: ΔΨm: mitochondrial transmembrane inner potential; AAU: autophagy arbitrary units; ATG5, autophagy related 5; ATG7: autophagy related 7; BAF: bafilomycin A1; BSA: bovine serum albumin; CASP3: caspase 3; CF: carboxyfluorescein; CTSB: cathepsin B; CVS: crystal violet staining; DCF: dichlorofluorescein; DCFH2: 2',7'-dichlorodihydrofluorescein; DMMB: 1,9-dimethyl methylene blue; ER: endoplasmic reticulum; HaCaT: non-malignant immortal keratinocyte cell line from adult human skin; HP: hydrogen peroxide; LC3B-II: microtubule associated protein 1 light chain 3 beta-II; LMP: lysosomal membrane permeabilization; LTG: LysoTracker™ Green DND-26; LTR: LysoTracker™ Red DND-99; 3-MA: 3-methyladenine; MB: methylene blue; mtDNA: mitochondrial DNA; MitoSOX™: red mitochondrial superoxide probe; MTDR: MitoTracker™ Deep Red FM; MTO: MitoTracker™ Orange CMTMRos; MT-ND1: mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 1; MTT: methylthiazolyldiphenyl-tetrazolium bromide; 1O2: singlet oxygen; OH. hydroxil radical; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; PBS: phosphate-buffered saline; PI: propidium iodide; PDT: photodynamic therapy; PS: photosensitizer; QPCR: gene-specific quantitative PCR-based; Rh123: rhodamine 123; ROS: reactive oxygen species RTN: rotenone; SQSTM1/p62: sequestosome 1; SUVs: small unilamellar vesicles; TBS: Tris-buffered saline.

Photo-Oxidation of Unilamellar Vesicles by a Lipophilic Pterin: Deciphering Biomembrane Photodamage

Pterins are natural products that can photosensitize the oxidation of DNA, proteins, and phospholipids. Recently, a new series of decyl-chain (i.e., lipophilic) pterins were synthesized and their photophysical properties were investigated. These decyl-pterins led to efficient intercalation in large unilamellar vesicles and produced, under UVA irradiation, singlet molecular oxygen, a highly oxidative species that react with polyunsaturated fatty acids (PUFAs) to form hydroperoxides. Here, we demonstrate that the association of 4-(decyloxy)pteridin-2-amine ( O-decyl-Ptr) to lipid membranes is key to its ability to trigger phospholipid oxidation in unilamellar vesicles of phosphatidylcholine rich in PUFAs used as model biomembranes. Our results show that O-decyl-Ptr is at least 1 order of magnitude more efficient photosensitizer of lipids than pterin (Ptr), the unsubstituted derivative of the pterin family, which is more hydrophilic and freely passes across lipid membranes. Lipid peroxidation photosensitized by O-decyl-Ptr was detected by the formation of conjugated dienes and oxidized lipids, such as hydroxy and hydroperoxide derivatives. These primary products undergo a rapid conversion into short-chain secondary products by cleavage of the fatty-acid chains, some of which are due to subsequent photosensitized reactions. As a consequence, a fast increase in membrane permeability is observed. Therefore, lipid oxidation induced by O-decyl-Ptr could promote cell photodamage due to the biomembrane integrity loss, which in turn may trigger cell death.

Antimicrobial Peptide K0-W6-Hya1 Induces Stable Structurally Modified Lipid Domains in Anionic Membranes

Considering the known different mode of action of antimicrobial peptides in zwitterionic and anionic cell membranes, the present work compares the action of the antimicrobial peptide K⁰-W⁶-Hya1 (KIFGAIWPLALGALKNLIK-NH₂) with zwitterionic and negatively charged model membranes, namely, liposomes composed of phosphatidylcholine (PC) and phosphatidylglycerol (PG) membranes, and a mixture of the two. Differential scanning calorimetry (DSC), steady state fluorescence of the Trp residue, dynamic light scattering (DLS), and measurement of the leakage of an entrapped fluorescent dye (carboxyfluorescein, CF) were performed with large unilamellar vesicles (LUVs). All techniques evidenced the different action of the peptide in zwitterionic and anionic vesicles. Trp fluorescence spectroscopy shows that the differences are related not only to the partition of the cationic peptide in zwitterionic and anionic membranes, but also to the different penetration depth of the peptide into the lipid bilayers: Trp goes deeper into negatively charged membranes, both in the gel and fluid phases, than into zwitterionic ones. DSC shows that the peptide is strongly attached to anionic bilayers, giving rise to the coexistence of two different lipid regions, one depleted of peptide and another one peptide-disturbed, possibly a stable or transient polar pore, considering the leakage of CF. This contrasts with the homogeneous effect produced by the peptide in zwitterionic membranes, probably related to peptide-membrane diffusion. Moreover, in mixed bilayers (PC:PG), the peptide sequesters negatively charged lipids, creating peptide-rich anionic lipid regions, strongly disturbing the membrane. The distinct structural interaction displayed by the peptide in PC and PG membranes could be related to the different mechanisms of action of the peptide in anionic prokaryotic and zwitterionic eukaryotic cell membranes.

Proteomic and transcriptomic analysis of saliva components from the hematophagous reduviid Triatoma pallidipennis

Species belonging to the Triatominae subfamily are commonly associated with Chagas disease, as they are potential vectors of the parasite Trypanosoma cruzi. However, their saliva contains a cocktail of diverse anti-hemostatic proteins that prevent blood coagulation, vasodilation and platelet aggregation of blood; components with indisputable therapeutic potential. We performed a transcriptomic and proteomic analyses of salivary glands and protein spots from 2DE gels of milked saliva, respectively, from the Mexican Triatoma pallidipennis. Massive sequencing techniques were used to reveal this protein diversity. A total of 78 out of 233 transcripts were identified as proteins in the saliva, divided among 43 of 55 spots from 2DE gels of saliva, identified by LC-MS/MS analysis. Some of the annotated transcripts putatively code for anti-hemostatic proteins, which share sequence similarities with proteins previously described for South American triatomines. The most abundant as well as diverse transcripts and proteins in the saliva were the anti-hemostatic triabins. For the first time, a transcriptomic analysis uncovered other unrelated but relevant components in triatomines, including antimicrobial and thrombolytic polypeptides. Likewise, unique proteins such as the angiotensin-converting enzyme were identified not just in the salivary gland transcriptome but also at saliva proteome of this North American bloodsucking insect.

BIOLOGICAL SIGNIFICANCE

This manuscript is the first report of the correlation between proteome and transcriptome of Triatoma pallidipennis, which shows for the first time the presence of proteins in this insect that have not been characterized in other species of this family. This information contributes to a better understanding of the multiple host defense mechanisms that are being affected at the moment of blood ingestion by the insect. Furthermore, this report gives a repertoire of possible therapeutic proteins.

Melt With This Kiss: Paralyzing and Liquefying Venom of The Assassin Bug Pristhesancus plagipennis (Hemiptera: Reduviidae)

Assassin bugs (Hemiptera: Heteroptera: Reduviidae) are venomous insects, most of which prey on invertebrates. Assassin bug venom has features in common with venoms from other animals, such as paralyzing and lethal activity when injected, and a molecular composition that includes disulfide-rich peptide neurotoxins. Uniquely, this venom also has strong liquefying activity that has been hypothesized to facilitate feeding through the narrow channel of the proboscis-a structure inherited from sap- and phloem-feeding phytophagous hemipterans and adapted during the evolution of Heteroptera into a fang and feeding structure. However, further understanding of the function of assassin bug venom is impeded by the lack of proteomic studies detailing its molecular composition.By using a combined transcriptomic/proteomic approach, we show that the venom proteome of the harpactorine assassin bug Pristhesancus plagipennis includes a complex suite of >100 proteins comprising disulfide-rich peptides, CUB domain proteins, cystatins, putative cytolytic toxins, triabin-like protein, odorant-binding protein, S1 proteases, catabolic enzymes, putative nutrient-binding proteins, plus eight families of proteins without homology to characterized proteins. S1 proteases, CUB domain proteins, putative cytolytic toxins, and other novel proteins in the 10-16-kDa mass range, were the most abundant venom components. Thus, in addition to putative neurotoxins, assassin bug venom includes a high proportion of enzymatic and cytolytic venom components likely to be well suited to tissue liquefaction. Our results also provide insight into the trophic switch to blood-feeding by the kissing bugs (Reduviidae: Triatominae). Although some protein families such as triabins occur in the venoms of both predaceous and blood-feeding reduviids, the composition of venoms produced by these two groups is revealed to differ markedly. These results provide insights into the venom evolution in the insect suborder Heteroptera.

Venoms of Heteropteran Insects: A Treasure Trove of Diverse Pharmacological Toolkits

The piercing-sucking mouthparts of the true bugs (Insecta: Hemiptera: Heteroptera) have allowed diversification from a plant-feeding ancestor into a wide range of trophic strategies that include predation and blood-feeding. Crucial to the success of each of these strategies is the injection of venom. Here we review the current state of knowledge with regard to heteropteran venoms. Predaceous species produce venoms that induce rapid paralysis and liquefaction. These venoms are powerfully insecticidal, and may cause paralysis or death when injected into vertebrates. Disulfide-rich peptides, bioactive phospholipids, small molecules such as N,N-dimethylaniline and 1,2,5-trithiepane, and toxic enzymes such as phospholipase A2, have been reported in predatory venoms. However, the detailed composition and molecular targets of predatory venoms are largely unknown. In contrast, recent research into blood-feeding heteropterans has revealed the structure and function of many protein and non-protein components that facilitate acquisition of blood meals. Blood-feeding venoms lack paralytic or liquefying activity but instead are cocktails of pharmacological modulators that disable the host haemostatic systems simultaneously at multiple points. The multiple ways venom is used by heteropterans suggests that further study will reveal heteropteran venom components with a wide range of bioactivities that may be recruited for use as bioinsecticides, human therapeutics, and pharmacological tools.

Structure-activity relationship of the antimicrobial peptide gomesin: the role of peptide hydrophobicity in its interaction with model membranes

Antimicrobial peptides are part of the innate immune system of animals and plants. Their lytic activity against microorganisms generally depends on their ability to disrupt and permeabilize membranes. Here we study the structure-activity relationship of the antimicrobial peptide gomesin (Gm), from the spider Acanthoscurria gomesiana, with large unilamellar vesicles (LUVs) composed of 3:7 palmitoyloleoyl phosphatidylglycerol: palmitoyloleoyl phosphatidylcholine. Several synthetic analogues of Gm were designed to alter the hydrophobicity/charge of the molecule, whereby selected amino acid residues were replaced by alanine. Isothermal titration calorimetry (ITC) was used to assess the thermodynamic parameters of peptide binding to LUVs and light scattering measurements were made to evaluated peptide-induced vesicle aggregation. The ability of the peptides to permeabilize vesicles was quantified through the leakage of an entrapped fluorescent probe. The activity of peptides could be quantified in terms of the leakage extent induced and their affinity to the membrane, which was largely dictated by the exothermic enthalpy change. The results show that analogues more hydrophobic than Gm display higher activity, whereas peptides more hydrophilic than Gm have their activity almost abolished. Vesicle aggregation, on the other hand, largely increases with peptide charge. We conclude that interaction of Gm with membranes depends on an interplay between surface electrostatic interactions, which drive anchoring to the membrane surface and vesicle aggregation, and insertion of the hydrophobic portion into the membrane core, responsible for causing membrane rupture/permeabilization.

Interactome: Smart hematophagous triatomine salivary gland molecules counteract human hemostasis during meal acquisition

Human populations are constantly plagued by hematophagous insects' bites, in particular the triatomine insects that are vectors of the Trypanosoma cruzi agent in Chagas disease. The pharmacologically-active molecules present in the salivary glands of hematophagous insects are injected into the human skin to initiate acquisition of blood meals. Sets of vasodilators, anti-platelet aggregators, anti-coagulants, immunogenic polypeptides, anesthetics, odorants, antibiotics, and detoxifying molecules have been disclosed with the aid of proteomics and recombinant cDNA techniques. These molecules can provide insights about the insect-pathogen-host interactions essential for understanding the physiopathology of the insect bite. The data and information presented in this review aim for the development of new drugs to prevent insect bites and the insect-transmitted endemic of Chagas disease.

Interactions between intestinal compounds of triatomines and Trypanosoma cruzi

Triatomine bugs are vectors of Trypanosoma cruzi, the etiologic agent of Chagas disease, a devastating disease that disables and leads to the death of many people in Latin America. In this review, factors from the insect vector are described, including digestive enzymes, hemolysins, agglutinins, microbiota and especially antimicrobial factors, which are potentially involved in regulating the development of T. cruzi in the gut. Differential regulation of parasite populations shows that some triatomine defense reactions discriminate not only between molecular signals specific for trypanosome infections but also between different strains of T. cruzi.

Interactions of antimicrobial peptides with Leishmania and trypanosomes and their functional role in host parasitism

Antimicrobial peptides (AMPs) are multifunctional components of the innate systems of both insect and mammalian hosts of the pathogenic trypanosomatids Leishmania and Trypanosoma species. Structurally diverse AMPs from a wide range of organisms have in vitro activity against these parasites acting mainly to disrupt surface-membranes. In some cases AMPs also localize intracellularly to affect calcium levels, mitochondrial function and induce autophagy, necrosis and apoptosis. In this review we discuss the work done in the area of AMP interactions with trypanosomatid protozoa, propose potential targets of AMP activity at the cellular level and discuss how AMPs might influence parasite growth and differentiation in their hosts to determine the outcome of natural infection.