Purification and characterization of phospholipase A from the venom of Naja nigricollis

Harnessing snake venom phospholipases A2 to novel approaches for overcoming antibiotic resistance

The emergence of antibiotic resistance drives an essential race against time to reveal new molecular structures capable of addressing this alarming global health problem. Snake venoms are natural catalogs of multifunctional toxins and privileged frameworks, which serve as potential templates for the inspiration of novel treatment strategies for combating antibiotic resistant bacteria. Phospholipases A₂ (PLA₂ s) are one of the main classes of antibacterial biomolecules, with recognized therapeutic value, found in these valuable secretions. Recently, a number of biomimetic oligopeptides based on small fragments of primary structure from PLA₂ toxins has emerged as a meaningful opportunity to overcome multidrug-resistant clinical isolates. Thus, this review will highlight the biochemical and structural properties of antibacterial PLA₂ s and peptides thereof, as well as their possible molecular mechanisms of action and key roles in development of effective therapeutic strategies. Chemical strategies possibly useful to convert antibacterial peptides from PLA₂ s to efficient drugs will be equally addressed.

Purification and characterization of a phospholipase A2 from Cerastes cerastes (horn viper) snake venom

A single phospholipase A2 has been found in Cerastes cerastes venom, purified to homogeneity by a combination of chromatographic steps involving gel filtration on Sephadex G-50 and ion-exchange chromatography on DEAE-Sephadex A-50. Its mol. wt, its amino acid composition and its partial amino acid sequence have been determined. High homologies between its sequence and those of other Viperid phospholipides A2 have been noticed. The phospholipase was non-lethal to mice up to a dose as high as 25 mg/kg by i.p. and i.v. injection. This non-toxic enzyme exhibited an acidic isoelectric point and hydrolyzed monolayers of different short chain phospholipids. Some kinetic parameters have been studied potentiometric titration (with or without Triton X-100) and the rate of catalysis seemed not to be affected by changes in the physical state of the substrate.

Ocular effects of the venom from the spitting cobra (Naja nigricollis)

N. nigricollis venom caused transient corneal oedema, extensive chemosis and pupillary dilation when applied topically to the corneas of albino and pigmented rabbits. After 1 month, permanent corneal scarring, neovascularization and deepithelialization was noted in albino eyes, whereas minimal scarring or deepithelialization occurred in pigmented eyes. In contrast, mydriasis and cycloplegia occurred initially in the pigmented eye, with the pupil remaining fixed and dilated for more than 7 days. The albino pupil, however, returned to normal within 2-3 days. Preliminary penetration studies using labelled venom revealed that N. nigricollis venom was mainly bound in the corneal stroma of the albino eye and showed poor penetration, whereas minimal corneal binding and poor penetration was noted in the pigmented eye. It appears that the high initial corneal edema may result from the intrinsic release of histamine and acetylcholine. The progression of corneal edema to liquefaction and opacification is probably due to the release of an endogenous corneal damaging factor by the venom presumably a collagenase or proteinase. Treatment with corticosteroids significantly increased the severity of the keratoconjunctivitis and deepithelialization, whereas treatment with heparin significantly reduced the keratoconjunctivitis and prevented further opacification. It is postulated that heparin might act through its chelating effect on ions necessary for the action of the proteolytic enzymes.

Enhancement of adenosine 3',5'-monophosphate in human mononuclear and polymorphonuclear leukocytes by snake venoms

Snake venoms contain compound(s) that enhanced cyclic AMP content in human mononuclear leukocytes maximally after 5 min of incubation at 37 degrees C. The effect was time- and dose-dependent. The half-maximal stimulation of cyclic AMP production by black cobra venom was found at 0.45 micrograms of venom/ml and the value of the Hill coefficient was 0.7. The black cobra venom enhanced the cyclic AMP content in the cells at 4, 22, and 37 degrees C. Similar increase in the cyclic AMP content by six snake venoms was found in human polymorphonuclear leukocytes. The most active venom was from puff adder (Bitis arietans). The data suggest that one of the effects of the snake venoms may be rapid enhancement of cyclic AMP level in the affected cells.

A further examination of the active form of Crotalus adamanteus phospholipase A2

The phospholipase A2 from Crotalus adamanteus venom has been shown to be active as the dimer or 30 000 molecular weight species, at concentrations used for enzyme assay (0.1--10 microgram/ml). Gel filtration of the enzyme in the presence of Ca2+ and monomeric concentrations of the substrate dihexanoylphosphatidylcholine showed that all the protein migrated as a 30 000 molecular weight species. Active enzyme sedimentation velocity experiments using the same conditions gave s020,W=2.85 +/- 0.05 S, which compares favorably with the value obtained at mg/ml concentrations (3.11 S). These results confirm the results of Shen et al. (Shen, B.W., Tsao, F.H.C, Law, J.H. and Kézdy, F.J. (1975) J. Am. Chem. Soc. 97, 1205--1208).

Membrane asymmetry. A survey and critical appraisal of the methodology. II. Methods for assessing the unequal distribution of lipids

In the companion paper, I have reviewed the techniques employed for assessment of the asymmetric distribution and orientation of membrane proteins. This article deals with methods applicable to the investigation of the unequal distribution of lipids between the two membrane leaflets. Among the techniques I will discuss are the use of immunological techniques and lectins, chemical reagents, enzymatic isotopic labeling and degradation of membrane lipids, exchange proteins and physical techniques. Whenever appropriate, problems of crypticity and non-availability of lipids to interact with the appropriate ligands, reagents, modifying enzymes or exchange proteins have been envisaged. It appears that in many case, highly discordant results, sometimes with the same biological material, have been obtained. Some of the difficulties encountered presumably stem from the reported existence of non-bilayer arrangements and isotropic movement of lipids as evidenced by freeze-fracture and NMR studies. Other problems may be related to the induction of such arrangements, especially the inverted micellar arrangement, by the modifying agents, particularly degradation enzymes or exchange proteins when they cause severe unilateral modification of the lipids of the exposed leaflet. In addition, the situation is complicated by the role of the induced increase in the flip-flop rate under different experimental conditions and by modification of the rearrangement of lipid molecules as a result of the metabolic state of the cell or ghost preparation and of the reactivity of lipids as a consequence of temperature changes. Here, more so than with proteins, one must be cautious in interpreting experimental results. Moreover, it would appear that the use of different techniques in conjunction and the consequent comparison of results should be recommended. It has been emphasized that 'general rules' do not hold and that each new material should be assay again. To give one example, it is not pertinent to state that proteins enhance the flip-flop rate in lipid vesicles (and hence in membranes). This holds true for glycophorin from erythrocyte membrane, but could not be proved when mitochondrial cytochrome oxidase was used. There seems to be no rule for the distribution of lipids between the two leaflets of different membranes. For example, even for different strains of the same bacterial species, highly divergent results have been reported. It is generally (and probably under the influence of different studies with erythrocytes) believed that in mammalian plasma membranes, choline phospholipids are enriched in the outer leaflet and aminophospholipids in the inner leaflet. Though this contention may prove to be correct, different instances of contradictory results have been given in the text. This shows that if rules do exist, they remain to be discovered or established...

Chemical modification of the histidine residue in basic phospholipase A2 from the venom of Naja nigricollis

Phospholipase A2 from Naja nigricollis venom was separated into three fractions by chromatography on a column of CM-Sephadex C-25. The pI values of fractions CMS-5, CMS-6 and CMS-9 were determined to be 7.6, 8.3 and 10.6, respectively. Fraction CMS-9 was further purified on a DEAE-Sephacel column and the homogeneity was verified. The specific activity of CMS-9 was found to be 1300 units per mg and lethal toxicity 0.3 mg per kg mouse. The most basic and toxic fraction, CMS-9, was subjected to chemical modification with p-bromophenzcyl bromide. The enzyme lost both the enzyme activity and lethal toxicity, however, the antigenicity remained unchanged. Although both 8-anilinonaphthalenesulfonate and Ca2+ showed pronounced protection on the inactivation process, the mechanism of 8-anilinonaphthalene-sulfonate protection is different from that of Ca2+. Amino acid analysis showed that only one (His-47) out of three histidine residues was modified. Although both native and His-modified CMS-9 were perturbed by the presence of Ca2+, the modified enzyme lost the characteristic tryptophan blue shift suggesting that the modified enzyme is unable to exert a charge effect upon Ca2+ binding in the vicinity of the tryptophan group. Scatchard plots revealed only one type of binding sites for 8-anilinonaphthalenesulfonate in the presence of Ca2+. On the other hand, the modified enzyme lost the ability to bind 8-anilinonaphthalene. It is suggested tentatively that the hydrophobic pocket in which 8-anilinonaphthalenesulfonate is bound may be the site of the enzyme that interacts with phospholipid.

Preservation of bilayer structure in human erythrocytes and erythrocyte ghosts after phospholipase treatment. A 31P-NMR study

1. Fresh human erythrocytes were treated with lytic and non-lytic combinations of phospholipases A2, C and sphingomyelinase. The 31P-NMR spectra of ghosts derived from such erythrocytes show that, in all cases, the residual phospholipids and lysophospholipids remain organized in a bilayer configuration. 2. A bilayer configuration of the (lyso)phospholipids was also observed after treatment of erythrocyte ghosts with various phospholipases even in the case that 98% of the phospholipid was converted into lysophospholipid (72%) and ceramides (26%). 3. A slightly decreased order of the phosphate group of phospholipid molecules, seen as reduced effective chemical shift anisotropy in the 31P-NMR spectra, was found following the formation of diacyglycerols and ceramides in the membrane of intact erythrocytes. Treatment of ghosts always resulted in an extensive decrease in the order of the phosphate groups. 4. The results allow the following conclusions to made: a. Hydrolysis of phospholipids in intact red cells and ghosts does not result in the formation of non-bilayer configuration of residual phospholipids and lysophospholipids. b. Haemolysis, which is obtained by subsequent treatment of intact cells with sphingomyelinase and phospholipase A2, or with phospholipase C, cannot be ascribed to the formation of non-bilayer configuration of phosphate-containing lipids. c. Preservation of bilayer structure, even after hydrolysis of all phospholipid, shows that other membrane constitutents, e.g. cholesterol and/or membrane proteins play an important role in stabilizing the structure of the erythrocyte membrane. d. A major prerequisite for the application of phospholipases in lipid localization studies, the preservation of a bilayer configuration during phospholipid hydrolysis, is met for the erythrocyte membrane.

Purification and characterization of the anticoagulant principle of Trimeresurus mucrosquamatus venom

By means of CM-Sephadex column chromatography, Trimeresurus mucrosquamatus venom was separated into 20 fractions. Fraction XX had the marked anticoagulant action. This fraction was refractionated three times on Sephadex G-75, and a single peak was obtained. The patterns of microzone and disc electrophoresis also showed a single band. A single, symmetrical boundary with a value of 1.61 S was obtained by ultracentrifugation. It was a single peptide chain with a molecular weight of 11 700. The isoelectric point was higher than pH 10. The anticoagulant principle possessed phospholipase A activity and was calcium ion dependent. It did not possess proteolytic, tosyl-L-arginine methyl ester esterase, phosphodiesterase and alkaline phosphomonoesterase activities of the crude venom. The phospholipase A activity was heat-labile at pH 7.4, but was heat-stable at pH 5.6. The anticoagulant activity was more resistant to heat treatment as compared with phospholipase A activity. The anitoagulant action of the purified principle was competitively inhibited by platelet phospholid, tissue thromboplastin and cephalin, and was neutralized by antiserum. The anticoagulant principle inhibited platelet aggregation induced by ADP. It did not destroy fibrinogen, Factor X, prothrombin and thrombin; nor did it induce fibrinolysis nor interfere with the interaction between thrombin and fibrinogen. It is concluded that the anticoagulant action of this phospholipase A was due to the inhibition of the activations of Factors X and II through the inactivation of the procoagulant activity of phospholipids mediated partly by phospholipid-binding activity of this venom enzyme and partly by its enzymatic hydrolysis of phospholipids.

Naja mossambica mossambica venom. Purification, some properties and the amino acid sequences of three phospholipases A (CM-I, CM-II and CM-III)

Three phospholipases A, CM-I, CM-II and CM-III, were purified from Naja mossambica mossambica venom by gel filtration on Sephadex G-50 followed by ion-exchange chromatography on CM-cellulose. They comprise each 118 amino acid residues and are close-linked by seven intrachain disulphide bridges. The complete primary structure of the three phospholipases A have been elucidated. The sequences and the invariant amino acid residues of CM-I, CM-II and CM-III resemble those of phospholipases A from other snake venoms and also from porcine pancreas. However, the letality (LD50 values) of the three phospholipases A from Naja mossambica mossambica venom, differ among themselves, and are also much higher than the LD100 value encountered for notexin from Notechis scutatus scutatus venom.

Isolation and characterization of three phospholipases A from the crotoxin complex

1. Three phospholipases A (phosphatide acyl-hydrolase, EC 3.1.1.4) have been isolated from the crotoxin complex, the main toxic compound of the Crotalus durissus terrificus venom. 2. Two basic phospholipases A were highly purified from the crotoxin complex by single chromatography on carboxymethyl cellulose. The yields were 10% and 38% (w/w), respectively. They showed no differences with regard to isoelectric point, enzymatic activity, immunological properties, and toxicity. One acidic phospholipase A, purified to a final yield of 1-3% by chromatography on carboxymethyl cellulose, gel filtration on Sephadex G-50, and chromatography on DEAE-cellulose, was found to have one third of the specific enzymatic activity of the basic enzymes. The acidic phospholipase A was nontoxic and antigenically different from the basic enzymes. 3. Crotapotin, an acidic peptide of the crotoxin complex (31% yield, w/w), potentiated the toxicity and inhibited the enzymatic activity of the basic phospholipase A isoenzymes, but did not interact with the acidic phospholipase A. 4. The purified enzymes were homogeneous with respect to cellogel electrophoresis, polyacrylamide gel electrophoresis, dodecyl sulfate-gel electrophoresis, immunoelectrophoresis, and isoelectric focusing. 5. The molecular weights of the three phospholipases were found to be in the same range as determined by gel filtration in 6 M guanidine - HCl (14 500) and dodecyl sulfate-gel electrophoresis (15 800). The isoelectric points of these enzymes were at 9.7 and 4.8 for the first two and the third, respectivlar. The acidic enzyme contained more acidic instead of basic amino acid residues. The two methionine residues of each phospholipase were found to be positioned nearby the NH2 - and the C-terminal of the protein chains. A third methionine residue was demonstrated in the acidic phospholipase A. Fingerprint maps of the basic enzymes showed only slight differences. 7. NH2 - and C-terminal sequence analyses indicated a striking homology between the three Crotalus phospholipase A isoenzymes and several phospholipases from other sources.

Naja melanoleuca (forest cobra) venom. Purification and some properties of phospholipases A

Three phospholipases A (Fractions DE-I, DE-II and DE-III) were purified from Naja melanoleuca (Forest cobra) venom by a combination of gel filtration on Sephadex G-50 and chromatography on DEAE-cellulosemthe purified phospholipases A were homogeneous by various physicochemical criteria. Whereas Fraction DE-I contains 118 amino acid residues, Fractions DE-II and DE-III comprise 119 residues. The three enzymes are cross-linked by seven disulphide bridges, have asparagine as N-terminal amino acid and the C-terminal is glutamic acid or glutamine. The molecular weights of the three phospholipases A from sedimentation analysis at pH 2.1, also by the sodium dodecylsulphate-gel method and calculated from the amino acid composition, were close to 13 000. Studies of circular dichroism in the spectral region between 195 to 305 nm showed that the three phospholipases A contain similar helical contents but revealed conformational differences between their side-chain chromophores.