Insect Venom Peptides

Regulated processing and secretion of a peptide precursor in cilia

Cilia are sensory and secretory organelles that both receive information from the environment and transmit signals. Cilia-derived vesicles (ectosomes), formed by outward budding of the ciliary membrane, carry enzymes and other bioactive products; this process represents an ancient mode of regulated secretion. Peptidergic intercellular communication controls a wide range of physiological and behavioral responses and occurs throughout eukaryotes. The Chlamydomonas reinhardtii genome encodes what appear to be numerous prepropeptides and enzymes homologous to those used to convert metazoan prepropeptides into bioactive peptide products. Since C. reinhardtii, a green alga, lack the dense core vesicles in which metazoan peptides are processed and stored, we explored the hypothesis that propeptide processing and secretion occur through the regulated release of ciliary ectosomes. A synthetic peptide (GATI-amide) that could be generated from a 91-kDa peptide precursor (proGATI) serves as a chemotactic modulator, attracting minus gametes while repelling plus gametes. Here we dissect the processing pathway that leads to formation of an amidated peptidergic sexual signal specifically on the ciliary ectosomes of plus gametes. Unlike metazoan propeptides, modeling studies identified stable domains in proGATI. Mass spectrometric analysis of a potential prohormone convertase and the amidated proGATI-derived products found in cilia and mating ectosomes link endoproteolytic cleavage to ectosome entry. Extensive posttranslational modification of proGATI confers stability to its amidated product. Analysis of this pathway affords insight into the evolution of peptidergic signaling; this will facilitate studies of the secretory functions of metazoan cilia.

Antibacterial activities of two potential peptides extracted from Polistes wattii Cameron, 1900 (Vespidae: Polistinae) wasp venom collected at Eastern Province, Saudi Arabia

Alternatives of conventional antibiotics have become an urgent need to control drug-resistant bacteria. Therefore, search for new antibacterial agents has become a trend in several microbiological and pharmaceutical scientific works. Insects, one of the most successful and evolved species on earth is known to be an effective natural source of several medically useful chemicals including antibacterial agents. There is considerable evidence of using wasp venom against medical ailments in several parts of the world. In this work venom from Polistes wattii Cameron, 1900 collected from Eastern Province, Saudi Arabia was evaluated for its antibacterial activities. Such activity was tested against four pathogenic bacteria: two-gram positive Staphylococcus aureus (ATCC 25923) and Streptococcus mutans (RCMB 017(1) ATCC 25175) and two gram-negative (Salmonella typhimurium NCTC 12023 ATCC 14028 and Enterobacter cloacae (RCMB 001(1) ATCC 23355). Also, chemical characterization of wasp venom was done using HPLC and two isolated peptides were sequenced. The result indicates the potent anti-microbial effect of the venom against the four tested bacteria. The most sensitive bacteria were Staphylococcus aureus (ATCC 25923) and Streptococcus mutans (RCMB 017(1) ATCC 25175). The sequence of the two purified peptides indicates that they belong to mastoparan. The study results may pave way to use this wasp venom in future antibiotics especially in controlling skin infection by Staphylococcus aureus.

Interplay between membrane active host defense peptides and heme modulates their assemblies and in vitro activity

In the emerging era of antimicrobial resistance, the susceptibility to co-infections of patients suffering from either acquired or inherited hemolytic disorders can lead to dramatic increase in mortality rates. Closely related, heme liberated during hemolysis is one of the major sources of iron, which is vital for both host and invading microorganisms. While recent intensive research in the field has demonstrated that heme exerts diverse local effects including impairment of immune cells functions, it is almost completely unknown how it may compromise key molecules of our innate immune system, such as antimicrobial host defense peptides (HDPs). Since HDPs hold great promise as natural therapeutic agents against antibiotic-resistant microbes, understanding the effects that may modulate their action in microbial infection is crucial. Here we explore how hemin can interact directly with selected HDPs and influence their structure and membrane activity. It is revealed that induced helical folding, large assembly formation, and altered membrane activity is promoted by hemin. However, these effects showed variations depending mainly on peptide selectivity toward charged lipids, and the affinity of the peptide and hemin to lipid bilayers. Hemin-peptide complexes are sought to form semi-folded co-assemblies, which are present even with model membranes resembling mammalian or bacterial lipid compositions. In vitro cell-based toxicity assays supported that toxic effects of HDPs could be attenuated due to their assembly formation. These results are in line with our previous findings on peptide-lipid-small molecule systems suggesting that small molecules present in the complex in vivo milieu can regulate HDP function. Inversely, diverse effects of endogenous compounds could also be manipulated by HDPs.

Polybioside, a neuroactive compound from the venom of the social wasp Polybia paulista

Polybioside (1) was isolated from the venom of the social wasp Polybia paulista, and its structure was assigned as 3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl 3-(1H-imidazol-4-yl)propanimidate by NMR and MS protocols. The application of polybioside in rat brain, followed by the detection of c-Fos protein expression in some brain regions, indicated the compound is neuroactive in a number of brain areas. Polybioside causes convulsions in rats, even when peripherally applied.