Studies of phospholipase A and B activities of Egyptian snake venoms and a scorpion toxin

Enhancing Soluble Expression of Phospholipase B for Efficient Catalytic Synthesis of L-Alpha-Glycerylphosphorylcholine

Phospholipase B (PLB) harbors three distinct activities with broad substrate specificities and application fields. Its hydrolyzing of sn-1 and sn-2 acyl ester bonds enables it to catalyze the production of L-alpha-glycerylphosphorylcholine (L-α-GPC) from phosphatidylcholine (PC) without speed-limiting acyl migration. This work was intended to obtain high-level active PLB and apply it to establish an efficient system for L-α-GPC synthesis. PLB from Pseudomonas fluorescens was co-expressed with five different molecular chaperones, including trigger factor (Tf), GroEL-GroES (GroELS), DnaK-DnaJ-GrpE (DnaKJE), GroELS and DnaKJE, or GroELS and Tf or fused with maltose binding protein (MBP) in Escherichia coli BL21(DE3) to improve PLB expression. PLB with DnaKJE-assisted expression exhibited the highest catalytic activity. Further optimization of the expression conditions identified an optimal induction OD600 of 0.8, IPTG concentration of 0.3 mmol/L, induction time of 9 h, and temperature of 25 °C. The PLB activity reached a maximum of 524.64 ± 3.28 U/mg under optimal conditions. Subsequently, to establish an efficient PLB-catalyzed system for L-α-GPC synthesis, a series of organic-aqueous mixed systems and surfactant-supplemented aqueous systems were designed and constructed. Furthermore, the factors of temperature, reaction pH, metal ions, and substrate concentration were further systematically identified. Finally, a high yield of 90.50 ± 2.21% was obtained in a Span 60-supplemented aqueous system at 40 °C and pH 6.0 with 0.1 mmol/L of Mg2+. The proposed cost-effective PLB production and an environmentally friendly PLB-catalyzed system offer a candidate strategy for the industrial production of L-α-GPC.

The Sequence and Three-Dimensional Structure Characterization of Snake Venom Phospholipases B

Snake venom phospholipases B (SVPLBs) are the least studied enzymes. They constitute about 1% of Bothrops crude venoms, however, in other snake venoms, it is present in less than 1%. These enzymes are considered the most potent hemolytic agent in the venom. Currently, no structural information is available about these enzymes from snake venom. To better understand its three-dimensional structure and mechanisms of envenomation, the current work describes the first model-based structure report of this enzyme from Bothrops moojeni venom named as B. moojeni phospholipase B (PLB_Bm). The structure model of PLB_Bm was generated using model building software like I-TESSER, MODELLER 9v19, and Swiss-Model. The build PLB_Bm model was validated using validation tools (PROCHECK, ERRAT, and Verif3D). The analysis of the PLB_Bm modeled structure indicates that it contains 491 amino acid residues that form a well-defined four-layer αββα sandwich core and has a typical fold of the N-terminal nucleophile aminohydrolase (Ntn-hydrolase). The overall structure of PLB_Bm contains 18 β-strands and 17 α-helices with many connecting loops. The structure divides into two chains (A and B) after maturation. The A chain is smaller and contains 207 amino acid residues, whereas the B chain is larger and contains 266 amino acid residues. The sequence and structural comparison among homologous snake venom, bacterial, and mammals PLBs indicate that differences in the length and sequence composition may confer variable substrate specificity to these enzymes. Moreover, the surface charge distribution, average volume, and depth of the active site cavity also vary in these enzymes. The present work will provide more information about the structure-function relationship and mechanism of action of these enzymes in snakebite envenomation.

Proteomic Characterization of Two Medically Important Malaysian Snake Venoms, Calloselasma rhodostoma (Malayan Pit Viper) and Ophiophagus hannah (King Cobra)

Calloselasma rhodostoma (CR) and Ophiophagus hannah (OH) are two medically important snakes found in Malaysia. While some studies have described the biological properties of these venoms, feeding and environmental conditions also influence the concentration and distribution of snake venom toxins, resulting in variations in venom composition. Therefore, a combined proteomic approach using shotgun and gel filtration chromatography, analyzed by tandem mass spectrometry, was used to examine the composition of venoms from these Malaysian snakes. The analysis revealed 114 proteins (15 toxin families) and 176 proteins (20 toxin families) in Malaysian Calloselasma rhodostoma and Ophiophagus hannah species, respectively. Flavin monoamine oxidase, phospholipase A₂, phosphodiesterase, snake venom metalloproteinase, and serine protease toxin families were identified in both venoms. Aminopeptidase, glutaminyl-peptide cyclotransferase along with ankyrin repeats were identified for the first time in CR venom, and insulin, c-type lectins/snaclecs, hepatocyte growth factor, and macrophage colony-stimulating factor together with tumor necrosis factor were identified in OH venom for the first time. Our combined proteomic approach has identified a comprehensive arsenal of toxins in CR and OH venoms. These data may be utilized for improved antivenom production, understanding pathological effects of envenoming, and the discovery of biologically active peptides with medical and/or biotechnological value.

In-Depth Venome of the Brazilian Rattlesnake Crotalus durissus terrificus: An Integrative Approach Combining Its Venom Gland Transcriptome and Venom Proteome

Snake venoms are complex mixtures mainly composed of proteins and small peptides. Crotoxin is one of the most studied components from Crotalus venoms, but many other components are less known due to their low abundance. The venome of Crotalus durissus terrificus, the most lethal Brazilian snake, was investigated by combining its venom gland transcriptome and proteome to create a holistic database of venom compounds unraveling novel toxins. We constructed a cDNA library from C. d. terrificus venom gland using the Illumina platform and investigated its venom proteome through high resolution liquid chromotography-tandem mass spectrometry. After integrating data from both data sets, more than 30 venom components classes were identified by the transcriptomic analysis and 15 of them were detected in the venom proteome. However, few of them (PLA₂, SVMP, SVSP, and VEGF) were relatively abundant. Furthermore, only seven expressed transcripts contributed to ∼82% and ∼73% of the abundance in the transcriptome and proteome, respectively. Additionally, novel venom proteins are reported, and we highlight the importance of using different databases to perform the data integration and discuss the structure of the venom components-related transcripts identified. Concluding, this research paves the way for novel investigations and discovery of future pharmacological agents or targets in the antivenom therapy.

Some pharmacological studies on the effects of Cerastes vipera (Sahara sand viper) snake venom

The effects of the venom of the Sahara sand viper (Cerastes vipera) were studied on isolated chick biventer cervicis, isolated rat atria and vas deferens preparations, and on the electrocardiogram of anaesthetized rats. Effects on 3H-noradrenaline uptake were studied using rat brain synaptosomes. At 50 micrograms/ml and 100 micrograms/ml, the venom caused a transient increase in rate and force of contractions of the rat atria followed by an irreversible depression. These effects were not prevented by atenolol, atropine or a combination of the two. In the presence of 25 microM lignocaine, the effects of venom on rat atria were reversible by washing. At 100 micrograms/ml, the venom transiently increased responses of vas deferens preparations to indirect stimulation, but had little effect on responses to noradrenaline, KCl, and ATP. In the presence of an alpha 1-adrenoceptor antagonist (prazosin) or a P2-purinergic receptor antagonist (suramin), the venom still significantly increased twitch height and responses to noradrenaline but not to KCl or ATP. The effect of the venom did not change after exposure to a combination of prazosin, suramin and tetrodotoxin. The venom (100 micrograms/ml) significantly decreased twitches to indirect and direct stimulation in chick biventer cervicis preparations. Responses to exogenously applied acetylcholine, carbachol and KCl were also decreased. Venom blocked the synaptosomal uptake of 3H-noradrenaline (IC50 = 5 micrograms/ml), and caused severe bradycardia in vivo. Some of the direct effects on muscle preparations are possibly due to the venom's phospholipase A2 activity.

Interactions between membranes and cytolytic peptides

The physico-chemical and biological properties of cytolytic peptides derived from diverse living entities have been discussed. The principal sources of these agents are bacteria, higher fungi, cnidarians (coelenterates) and the venoms of snakes, insects and other arthropods. Attention has been directed to instances in which cytolytic peptides obtained from phylogenetically remote as well as from related sources show similarities in nature and/or mode of action (congeneric lysins). The manner in which cytolytic peptides interact with plasma membranes of eukaryotic cells, particularly the membranes of erythrocytes, has been discussed with emphasis on melittin, thiolactivated lysins and staphylococcal alpha-toxin. These and other lytic peptides are characterized in Table III. They can be broadly categorized into: (a) those which alter permeability to allow passage of ions, this process eventuating in colloid osmotic lysis, signs of which are a pre-lytic induction or latent period, pre-lytic leakage of potassium ions, cell swelling and inhibition of lysis by sucrose. Examples of lysins in which this mechanism is involved are staphylococcal alpha-toxin, streptolysin S and aerolysin; (b) phospholipases causing enzymic degradation of bilayer phospholipids as exemplified by phospholipases C of Cl. perfringens and certain other bacteria; (c) channel-forming agents such as helianthin, gramicidin and (probably) staphylococcal delta-toxin in which toxin molecules are thought to embed themselves in the membrane to form oligomeric transmembrane channels.

Isoelectric analysis of some Australian elapid snake venoms with special reference to phospholipase B and hemolysis

Venoms of the Australian elapid snakes Austrelaps superbus and Pseudechis colletti were analyzed in an electrofocusing column. A. superbus venom, little studied in the past, was found to have a mouse i.p. lethal potency of 0.48 mg/kg and to contain at least four lethal components. Venoms of both species had relatively high direct hemolytic activity for washed rabbit erythrocytes, as contrasted with venoms from 23 other species of snakes that were not hemolytic under the conditions used. Among venoms of the same 25 species, those of A. superbus and P. colletti produced turbidity in diluted egg yolk, those of Bungarus caeruleus and Bungarus multicinctus were quantitatively less active on egg yolk, whereas venoms of the 21 remaining species were negative. The component of the venoms responsible for egg yolk reactivity was partially purified and the preparations obtained were strongly active when tested with diluted egg yolk or with erythrocytes. Thin layer and paper chromatographic studies showed that these preparations possessed phospholipase B activity for phosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine and phosphatidylserine, but sphingomyelin was not degraded. The results suggest that hydrolysis of phosphatidylcholine is responsible for both egg yolk reactivity and hemolysis.

Envenoming by Cerastes viper - a report of two cases

Two cases of envenoming by Cerastes vipera are described Both were in snake collectors who were accidentally bitten on the finger while handling the snake. In both cases, local signs included a haemorrhagic bulla with fang marks, swelling and tenderness. These signs were mild in one case and moderately severe in the other, necessitating fasciotomy. No systemic signs were observed. Some coagulation abnormalities were found in both cases. In one, prolonged bleeding from the wound and a shortened euglobulin lysis time may suggest activation of the fibrinolytic mechanism. In the other, prolongation of prothrombin time occurred with no haemorrhagic diathesis. Treatment included fasciotomy in one case and elevation of the affected part and antibiotics in the other. It appears that the clinical course of this snakebite is relatively benign.

Lipolytic enzymes in bovine thyroid tissue. III. Lysophospholipase activity

Lysophospholipids are formed during phospholipid breakdown as a result of the action of phospholipases A. At certain concentrations these lysoderivatives destabilise biological membranes. Therefore, their concentration is of critical importance for membrane integrity. Prevention of lysophosphoglycerides accumulation may be the important role for lysophospholipases and is probably the explanation for their widespread occurrence in nature. Lysophospholipase activities were found in molds (Fairbairn, 1948), rice bran (Contardi & Ercoli, 1933), several microorganisms (Brockerhoff & Jensen, 1974), snake and bee venoms (Doery & Pearson, 1964; Mohamed et al., 1969; Shiloah et al., 1973), insects (Khan & Hodgson, 1967; Rao & Subrahmanyam, 1969), fish muscle (Yurkovski & Brockerhoff, 1965; Cohen et al., 1967) and in various animal tissues (Marples & Thompson, 1960). In mammalian tissue the enzyme was first described in beef pancreas (Shapiro, 1953). Relatively high levels were detected in intestine, lung, spleen, liver and pancreas, while lower levels were present in muscle, kidney, testes, brain and blood (Marples & Thompson, 1960). The presence of lysophospholipase activity in both supernatant and sediment of bovine thyroid was reported previously in relation to possible interference of this enzyme with the phospholipase A activity assay (De Wolf et al., 1976). The subcellular localization of bovine thyroid lysophospholipase and some properties of the membrane bound enzyme activity are discussed in this paper.

Role of cardiotoxin and phospholipase A in the blockade of nerve conduction and depolarization of skeletal muscle induced by cobra venom

1. The effects of phospholipase A (PhA), cardiotoxin (CTX) and neurotoxin (cobrotoxin) isolated from Formosan cobra (Naja naja atra) venom on conduction of the rat phrenic nerve and membrane potential of the rat diaphragm were studied.2. Phospholipase A, lysolecithin and cobrotoxin were without effect on the axonal conduction. Cardiotoxin was the only active agent in cobra venom, but it was less potent than the crude venom.3. The blocking action of cardiotoxin was markedly accelerated by the simultaneous administration of phospholipase A. However, the minimum effective concentration of cardiotoxin (100 mug/ml), was not decreased by phospholipase A. Pretreatment of the nerve with phospholipase A, followed by washout, did not alter the activity of cardiotoxin.4. Cardiotoxin (3 mug/ml) completely depolarized the membrane of superficial muscle fibres within 60 min, being 3 times more potent than the crude venom. Phospholipase A, on the other hand, needed a dose 30 times higher and a prolonged period of incubation to induce depolarization of similar extent. Cobrotoxin was without effect on membrane potentials.5. CaCl(2) (10 mM) effectively antagonized the nerve blocking as well as the depolarizing effect of the crude venom, cardiotoxin or cardiotoxin plus phospholipase A. By contrast, the slow depolarizing effect of phospholipase A was enhanced by high concentrations of calcium.6. Cardiotoxic fractions of Indian cobra venom affected both nerve conduction and diaphragm membrane potential in exactly the same way as cardiotoxin. Toxin A of the same venom was without effect.7. It is concluded that the active agent in cobra venoms either on axonal conduction or on muscle membrane is cardiotoxin. The synergistic effect of phospholipase A on cardiotoxin appears to be due to acceleration rather than potentiation of its action. The mechanism of action of cardiotoxin and its synergism by phospholipase A are discussed.