A lysine rich C-terminal tail is directly involved in the toxicity of CSTX-1, a neurotoxic peptide from the venom of the spider Cupiennius salei

The Dual Prey-Inactivation Strategy of Spiders-In-Depth Venomic Analysis of Cupiennius salei

Most knowledge of spider venom concerns neurotoxins acting on ion channels, whereas proteins and their significance for the envenomation process are neglected. The here presented comprehensive analysis of the venom gland transcriptome and proteome of Cupiennius salei focusses on proteins and cysteine-containing peptides and offers new insight into the structure and function of spider venom, here described as the dual prey-inactivation strategy. After venom injection, many enzymes and proteins, dominated by α-amylase, angiotensin-converting enzyme, and cysteine-rich secretory proteins, interact with main metabolic pathways, leading to a major disturbance of the cellular homeostasis. Hyaluronidase and cytolytic peptides destroy tissue and membranes, thus supporting the spread of other venom compounds. We detected 81 transcripts of neurotoxins from 13 peptide families, whereof two families comprise 93.7% of all cysteine-containing peptides. This raises the question of the importance of the other low-expressed peptide families. The identification of a venom gland-specific defensin-like peptide and an aga-toxin-like peptide in the hemocytes offers an important clue on the recruitment and neofunctionalization of body proteins and peptides as the origin of toxins.

Molecular basis of the remarkable species selectivity of an insecticidal sodium channel toxin from the African spider Augacephalus ezendami

The inexorable decline in the armament of registered chemical insecticides has stimulated research into environmentally-friendly alternatives. Insecticidal spider-venom peptides are promising candidates for bioinsecticide development but it is challenging to find peptides that are specific for targeted pests. In the present study, we isolated an insecticidal peptide (Ae1a) from venom of the African spider Augacephalus ezendami (family Theraphosidae). Injection of Ae1a into sheep blowflies (Lucilia cuprina) induced rapid but reversible paralysis. In striking contrast, Ae1a was lethal to closely related fruit flies (Drosophila melanogaster) but induced no adverse effects in the recalcitrant lepidopteran pest Helicoverpa armigera. Electrophysiological experiments revealed that Ae1a potently inhibits the voltage-gated sodium channel BgNa_V1 from the German cockroach Blattella germanica by shifting the threshold for channel activation to more depolarized potentials. In contrast, Ae1a failed to significantly affect sodium currents in dorsal unpaired median neurons from the American cockroach Periplaneta americana. We show that Ae1a interacts with the domain II voltage sensor and that sensitivity to the toxin is conferred by natural sequence variations in the S1–S2 loop of domain II. The phyletic specificity of Ae1a provides crucial information for development of sodium channel insecticides that target key insect pests without harming beneficial species.

Apocrine secretion: New insights into an old phenomenon

BACKGROUND

While apocrine secretion was among the earliest secretory mechanisms to be identified, its underlying basis remains poorly understood.

SCOPE OF REVIEW

This review reappraises our understanding of apocrine secretion using insights about apocrine secretion from the salivary glands of Drosophila, in which molecular genetic analyses have provided a glimmer of hope for elucidating the mechanistic aspects of this fundamental process.

MAJOR CONCLUSIONS

In contrast to the well-defined process of exocytosis, apocrine secretion is non-vesicular transport and secretory pathway that entails the loss of part of the cytoplasm. It often involves apical protrusions and generates cytoplasmic fragments inside a secretory lumen. In its most intense phase this process is accompanied by the release of large fragments of cellular structures and entire organelles that include mitochondria, Golgi, and portions of the endoplasmic reticulum, among others. Proteomic analyses revealed that the secretion is composed of hundreds to thousands of membranous, cytoskeletal, microsomal, mitochondrial, ribosomal, and even nuclear as well as nucleolar proteins. Strikingly, although many nuclear proteins are released, the nuclear deoxyribonucleic acid itself remains intact. In spite of this complexity, it appears that several protein components of apocrine secretion are identical, regardless of the location of the apocrine gland.

GENERAL SIGNIFICANCE

This type of secretion appears to be common to many, if not all, barrier epithelial tissues including skin derivatives and the epididymis, and is implicated also in lung/bronchi and intestinal epithelium. Apocrine secretion is a mechanism that provides the en masse delivery of a very complex proteinaceous mixture from polarized epithelial tissues to allow for communication at exterior interfaces.

Cysteine-rich toxins from Lachesana tarabaevi spider venom with amphiphilic C-terminal segments

Venom of Lachesana tarabaevi (Zodariidae, "ant spiders") exhibits high insect toxicity and serves a rich source of potential insecticides. Five new peptide toxins active against insects were isolated from the venom by means of liquid chromatography and named latartoxins (LtTx). Complete amino acid sequences of LtTx (60-71 residues) were established by a combination of Edman degradation, mass spectrometry and selective proteolysis. Three toxins have eight cysteine residues that form four intramolecular disulfide bridges, and two other molecules contain an additional cystine; three LtTx are C-terminally amidated. Latartoxins can be allocated to two groups with members similar to CSTX and LSTX toxins from Cupiennius salei (Ctenidae) and Lycosa singoriensis (Lycosidae). The interesting feature of the new toxins is their modular organization: they contain an N-terminal cysteine-rich (knottin or ICK) region as in many neurotoxins from spider venoms and a C-terminal linear part alike some cytolytic peptides. The C-terminal fragment of one of the most abundant toxins LtTx-1a was synthesized and shown to possess membrane-binding activity. It was found to assume amphipathic α-helical conformation in membrane-mimicking environment and exert antimicrobial activity at micromolar concentrations. The tails endow latartoxins with the ability to bind and damage membranes; LtTx show cytolytic activity in fly larvae neuromuscular preparations. We suggest a membrane-dependent mode of action for latartoxins with their C-terminal linear modules acting as anchoring devices.

A venom-derived neurotoxin, CsTx-1, from the spider Cupiennius salei exhibits cytolytic activities

CsTx-1, the main neurotoxic acting peptide in the venom of the spider Cupiennius salei, is composed of 74 amino acid residues, exhibits an inhibitory cysteine knot motif, and is further characterized by its highly cationic charged C terminus. Venom gland cDNA library analysis predicted a prepropeptide structure for CsTx-1 precursor. In the presence of trifluoroethanol, CsTx-1 and the long C-terminal part alone (CT1-long; Gly-45-Lys-74) exhibit an α-helical structure, as determined by CD measurements. CsTx-1 and CT1-long are insecticidal toward Drosophila flies and destroys Escherichia coli SBS 363 cells. CsTx-1 causes a stable and irreversible depolarization of insect larvae muscle cells and frog neuromuscular preparations, which seem to be receptor-independent. Furthermore, this membranolytic activity could be measured for Xenopus oocytes, in which CsTx-1 and CT1-long increase ion permeability non-specifically. These results support our assumption that the membranolytic activities of CsTx-1 are caused by its C-terminal tail, CT1-long. Together, CsTx-1 exhibits two different functions; as a neurotoxin it inhibits L-type Ca(2+) channels, and as a membranolytic peptide it destroys a variety of prokaryotic and eukaryotic cell membranes. Such a dualism is discussed as an important new mechanism for the evolution of spider venomous peptides.

Cupiennin 1a exhibits a remarkably broad, non-stereospecific cytolytic activity on bacteria, protozoan parasites, insects, and human cancer cells

Cupiennin 1a, a cytolytic peptide isolated from the venom of the spider Cupiennius salei, exhibits broad membranolytic activity towards bacteria, trypanosomes, and plasmodia, as well as human blood and cancer cells. In analysing the cytolytic activity of synthesised all-D: - and all-L: -cupiennin 1a towards pro- and eukaryotic cells, a stereospecific mode of membrane destruction could be excluded. The importance of negatively charged sialic acids on the outer leaflet of erythrocytes for the binding and haemolytic activity of L: -cupiennin 1a was demonstrated. Reducing the overall negative charges of erythrocytes by partially removing their sialic acids or by protecting them with tri- or pentalysine results in reduced haemolytic activity of the peptide.

Venomics of the spider Ornithoctonus huwena based on transcriptomic versus proteomic analysis

The spider Ornithoctonus huwena is a venomous spider found in southern China. Its venom is a complex mixture of numerous biologically active components. In this study, 41 novel unique transcripts encoding cellular proteins or other possible venom components were generated from the previously constructed cDNA library. These proteins were also annotated by KOG (eukaryotic orthologous group) and GO (gene ontology) terms. A novel cellular transcript contig encoding an EF-hand protein (named HWEFHP1) was found, which might be involved in the secretion of toxins in the venom glands. In order to have an overview of the molecular diversity of the O. huwena venom, the datasets of all the transcripts, peptides and proteins known so far were analyzed. A comparison of the data obtained through a proteomic versus a transcriptomic approach, revealed that only 15 putative cystine knot toxins (CKTs) were identified by both approaches, 29 transcripts coding for CKTs were found in the transcriptome but not as translated peptides in the venom proteome. However, no cellular protein with identical molecular weight was identified by both approaches. Our data may contribute to a deeper understanding of the biology and ecology of O. huwena and the relationship between structure and function of individual toxins.

Transcriptome analysis of the venom glands of the Chinese wolf spider Lycosa singoriensis

The wolf spider Lycosa singoriensis is a hunting spider with a widespread distribution in northwest China. The venom gland of spiders, which is a very specialized secretory tissue, can secrete abundant and complex toxin components. To extensively examine the transcripts expressed in the venom glands of L. singoriensis, we generated 833 expressed sequence tags (ESTs) from a directional cDNA library. Toxin-like sequences account for 69.1% of these ESTs, 17.3% are similar to cellular transcripts and 13.6% have no significant similarity to any known sequences. Here, we identified 223 novel toxin-like sequences, which can be classified into six different superfamilies; that means a novel potential source of ligands for varied ion channels was discovered. With the aid of Gene Ontology terms and homology to eukaryotic orthologous groups, the annotation of cellular transcripts revealed some cellular processes important for the toxin secretion of venom glands including protein synthesis, protein folding, tuned post-translational processing and trafficking, etc.

Comparison of the partial proteomes of the venoms of Brazilian spiders of the genus Phoneutria

The proteomes of the venoms of the Brazilian wandering "armed" spiders Phoneutria nigriventer, Phoneutria reidyi, and Phoneutria keyserlingi, were compared using two-dimensional gel electrophoresis. The venom components were also fractionated using a combination of preparative reverse phase HPLC on Vydac C4, analytical RP-HPLC on Vydac C8 and C18 and cation exchange FPLC on Resource S at pH 6.1 and 4.7, or anion exchange HPLC on Synchropak AX-300 at pH 8.6. The amino acid sequences of the native and S-pyridyl-ethylated proteins and peptides derived from them by enzymatic digestion and chemical cleavages were determined using a Shimadzu PPSQ-21(A) automated protein sequencer, and by MS/MS collision induced dissociations. To date nearly 400 peptides and proteins (1.2-27 kDa) have been isolated in a pure state and, of these, more than 100 have had their complete or partial amino acid sequences determined. These sequences demonstrate, as might be expected, that the venoms of P. reidyi and P. keyserlingi (Family: Ctenidae) both contain a similar range of isoforms of the neurotoxins as those previously isolated from P. nigriventer which are active on neuronal ion (Ca(2+), Na(+) and K(+)) channels and NMDA-type glutamate receptors. In addition two new families of small (3-4 kDa) toxins, some larger protein (>10 kDa) components, and two serine proteinases of the venom of P. nigriventer are described. These enzymes may be responsible for some of the post-translational modification observed in some of the venom components.

CSTX-13, a highly synergistically acting two-chain neurotoxic enhancer in the venom of the spider Cupiennius salei (Ctenidae)

The survival of the spider Cupiennius salei depends on its hunting success, which largely relies on its immediately paralyzing multicomponent venom. Here, we report on the isolation and characterization of CSTX-13, a neurotoxic enhancer in the spider venom. De novo elucidation of the disulfide bridge pattern of CSTX-13 and the neurotoxin CSTX-1 by tandem MS revealed an identical arrangement. However, in contrast to CSTX-1, CSTX-13 is a two-chain peptide with two interchain and two intrachain disulfide bridges. Furthermore, the insecticidal activity of CSTX-13 is synergistically increased in the presence of K+ ions as well as of the cytolytic peptide cupiennin 1a. We demonstrated that the weakly neurotoxic CSTX-13 enhances the paralytic activity of the neurotoxin CSTX-1 by 65% when it is administered with the latter at its entirely nontoxic physiological concentration, which is 440 times below its LD50 concentration.

Biochemistry, toxicology and ecology of the venom of the spider Cupiennius salei (Ctenidae)

The venom of Cupiennius salei consists of many low molecular compounds, nine neurotoxic acting peptides (CSTX), at least eight neurotoxic and cytolytic acting peptides (cupiennins), a highly active hyaluronidase, and several hitherto unidentified proteins. The structure of several peptides is given. A synergistic action between three main groups is proposed: injected into the prey tissue, the enzyme hyaluronidase acts as a spreading factor, thus, facilitating a better access of venom neurotoxins to their targets, cupiennins disturb cell membranes and influence cell excitability, through this augmenting the mere neurotoxic effect of CSTX-1 synergistically. The venom glands of an apocrine secretion type provide an average of 12 microl per milking (adult female). Venom sensitivity of arthropods differs between 0.001 and >20nl venom/mg insect. Regeneration time of an empty venom gland is approx. 2 weeks. Consequently, spiders may encounter situations in which they have to decide whether their limited venom storage is sufficient to kill a given prey item. Experiments are presented which show that C. salei knows the actual venom content of its venom glands. It injects no more venom than necessary. This coincides with an experimentally determined LD(50) value in harmless prey items, but C. salei injects more venom in aggressive or otherwise dangerous prey items (quantification of injected venom amounts by monoclonal antibodies). These results indicate that C. salei uses its venom as economically as possible and this supports our venom optimisation hypothesis.

Cupiennin 1d*: the cytolytic activity depends on the hydrophobic N-terminus and is modulated by the polar C-terminus

To investigate structural features modulating the biological activity of cupiennin 1 peptides from the spider Cupiennius salei, three truncated cupiennin 1d analogs were synthesized. The fact that their growth inhibiting effect on Gram-negative and Gram-positive bacteria, their lytic activity with human red blood cells and their insecticidal effect on Drosophila melanogaster correlates with structural properties shows that the hydrophobic N-terminal chain segment includes the major determinants of structure and activity. The polar C-terminus seems to modulate peptide accumulation at negatively charged cell surfaces via electrostatic interactions and has no important effect on the peptides' amphipathic secondary structure.

The venom optimisation hypothesis: a spider injects large venom quantities only into difficult prey types

The spider Cupiennius salei needs 0.01-10 microl venom to kill a prey item. Since its venom glands contain only 10 microl and regeneration requires 8-16 days C. salei should use its venom very economically. By a monoclonal antibody we measured, for the first time, the amounts of venom injected by a spider into different prey types. Crickets and stick insects, as victims without special defence mechanism, received only the minimum amount of venom which is not significantly different from the LD(50). Blowflies and ground beetles received considerably more venom because they are difficult to overwhelm or even endanger the spider by their defence behaviour. These results support our venom optimisation hypothesis which supposes that spiders use their venom as economically as possible.

Cupiennin 1, a new family of highly basic antimicrobial peptides in the venom of the spider Cupiennius salei (Ctenidae)

A new family of antimicrobial peptides was isolated from the venom of Cupiennius salei. The peptides were purified to homogeneity, and the sequence of cupiennin 1a was determined by Edman degradation: GFGALFKFLAKKVAKTVAKQAAKQGAKYVVNKQME-NH(2). The amino acid sequences of cupiennin 1b, c, and d were obtained by a combination of sequence analysis and mass spectrometric measurements of comparative tryptic peptide mapping. All peptides consist of 35 amino acid residues and are characterized by a more hydrophobic N-terminal chain region and a C terminus composed preferentially of polar and charged residues. The total charge of all cupiennins calculated under physiological conditions is +8, and their C terminus, formed by a glutamic acid residue, is amidated. Conformational studies of the peptides revealed a high helix forming potential. Antimicrobial assays on bacteria with cupiennin 1a, 1d, and synthesized cupiennins 1a* and 1d* showed minimal inhibitory concentrations for bacteria in the submicromolar range. Their lytic effect on human red blood cells was lower by a factor of 8 to 14 than the highly hemolytic melittin. Cupiennin 1a, 1b, 1d, 1a*, and 1d* showed pronounced insecticidal activity. The immediate biological effects and the structural properties of the isolated cupiennins indicate a membrane-destroying mode of action on prokaryotic as well as eukaryotic cells.

An examination of the potential role of spider digestive proteases as a causative factor in spider bite necrosis

Tissue necrosis following spider bites is a widespread problem. In the continental United States, the brown recluse (Loxosceles reclusa), hobo spider (Tegenaria agrestis), garden spider (Argiope aurantia) and Chiracanthium species, among others, reportedly cause such lesions. The exact mechanism producing such lesions is controversial. There is evidence for both venom sphingomyelinase and spider digestive collagenases. We have examined the role of spider digestive proteases in spider bite necrosis. The digestive fluid of A. aurantia was assayed for its ability to cleave a variety of connective tissue proteins, including collagen. Having confirmed that the fluid has collagenases, the digestive fluid was injected into the skin of rabbits to observe whether it would cause necrotic lesions. It did not. The data do not support the suggestions that spider digestive collagenases have a primary role in spider bite necrosis.