An agonist of CXCR4 induces a rapid recovery from the neurotoxic effects of Vipera ammodytes and Vipera aspis venoms.

People bitten by Alpine vipers are usually treated with antivenom antisera to prevent the noxious consequences caused by the injected venom. However, this treatment suffers from a number of drawbacks and additional therapies are necessary. The venoms of Vipera ammodytes and of Vipera aspis are neurotoxic and cause muscle paralysis by inducing neurodegeneration of motor axon terminals because they contain a presynaptic acting sPLA2 neurotoxin. We have recently found that any type of damage to motor axons is followed by the expression and activation of the intercellular signaling axis consisting of the CXCR4 receptor present on the membrane of the axon stump and of its ligand, the chemokine CXCL12 released by activated terminal Schwann cells. We show here that also V. ammodytes and V. aspis venoms cause the expression of the CXCL12-CXCR4 axis. We also show that a small molecule agonist of CXCR4, dubbed NUCC-390, induces a rapid regeneration of the motor axon terminal with functional recovery of the neuromuscular junction. These findings qualify NUCC-390 as a promising novel therapeutics capable of improving the recovery from the paralysis caused by the snakebite of the two neurotoxic Alpine vipers.

Size of silk fibroin ß-sheet domains affected by Ca2.

In the search for suitable scaffold materials for tissue regeneration, silk fibroin has become one of the most promising candidates due to its biocompatibility and good physical properties. To facilitate bone formation in osteochondral defects, it is often combined with a bone promoting additive. Here we demonstrate using HRTEM analysis how the release of Ca2+ ions from bioactive glass or Ca-salts results in the reduction of ß-sheet domain size that effectively controls a scaffold's properties, such as degradation and mechanical stiffness. We show that these changes already occur in silk fibroin solution prior to scaffold preparation and are caused by a decrease in zeta potential that forces fibroin molecules into tighter packing resulting in higher scaffold crystallinity, smaller ß-sheet domains and higher interconnectivity. The reduction of ß-sheet domains improves the elastic modulus and allows faster degradation despite the higher crystallinity. Ca2+ was also shown to be beneficial to the formation of hydroxy-apatite sheets on the fibroin surface.

The sensing of membrane microdomains based on pore-forming toxins.

Membrane rafts are transient and unstable membrane microdomains that are enriched in sphingolipids, cholesterol, and specific proteins. They are involved in intracellular trafficking, signal transduction, pathogen entry, and attachment of various ligands. Increasing experimental evidence on the crucial biological roles of membrane rafts under normal and pathological conditions require new techniques for their structural and functional characterization. In particular, fluorescence-labeled cytolytic proteins that interact specifically with molecules enriched in rafts are of increasing interest. Cholera toxin subunit B interacts specifically with raft-residing ganglioside G(M1), and it has long been the lipid probe of choice for membrane rafts. Recently, four new pore-forming toxins have been proposed as selective raft markers: (i) equinatoxin II, a cytolysin from the sea anemone Actinia equina, which specifically recognizes free and membrane-embedded sphingomyelin; (ii) a truncated non-toxic mutant of a cytolytic protein, lysenin, from the earthworm Eisenia foetida, which specifically recognizes sphingomyelin-enriched membrane domains; (iii) a non-toxic derivative of the cholesterol-dependent cytolysin perfringolysin O, from the bacterium Clostridium perfringens, which selectively binds to membrane domains enriched in cholesterol; and (iv) ostreolysin, from the mushroom Pleurotus ostreatus, which does not bind to a single raft-enriched lipid component, but requires a specific combination of two of the most important raft-residing lipids: sphingomyelin and cholesterol. Nontoxic, raft-binding derivatives of cytolytic proteins have already been successfully used to explore both the structure and function of membrane rafts, and of raft-associated molecules. Here, we review these four new derivatives of pore-forming toxins as new putative markers of these membrane microdomains.

Genetic interactions between a phospholipase A2 and the Rim101 pathway components in S. cerevisiae reveal a role for this pathway in response to changes in membrane composition and shape.

Modulating composition and shape of biological membranes is an emerging mode of regulation of cellular processes. We investigated the global effects that such perturbations have on a model eukaryotic cell. Phospholipases A(2) (PLA(2)s), enzymes that cleave one fatty acid molecule from membrane phospholipids, exert their biological activities through affecting both membrane composition and shape. We have conducted a genome-wide analysis of cellular effects of a PLA(2) in the yeast Saccharomyces cerevisiae as a model system. We demonstrate functional genetic and biochemical interactions between PLA(2) activity and the Rim101 signaling pathway in S. cerevisiae. Our results suggest that the composition and/or the shape of the endosomal membrane affect the Rim101 pathway. We describe a genetically and functionally related network, consisting of components of the Rim101 pathway and the prefoldin, retromer and SWR1 complexes, and predict its functional relation to PLA(2) activity in a model eukaryotic cell. This study provides a list of the players involved in the global response to changes in membrane composition and shape in a model eukaryotic cell, and further studies are needed to understand the precise molecular mechanisms connecting them.

Ultrastructural evidence for the uptake of a neurotoxic snake venom phospholipase A2 into mammalian motor nerve terminals.

A mutant form of ammodytoxin A, a neurotoxic phospholipase A(2) from the venom of the long nosed viper Vipera ammodytes ammodytes, was prepared by site-directed mutagenesis, conjugated to a nanogold particle and inoculated into the antero-lateral aspect of one hind limb of female mice. Eight hours later the mice were killed, the soleus muscles of both ipsi- and contra-lateral hind limbs were removed, exposed to a silver enhancing medium and then prepared for transmission electron microscopy. Silver-enhanced particles were subsequently found concentrated in the peri-synaptic area, particularly within the synaptic gutter and the deep synaptic folds, and in many cases had been taken up into the cytoplasm of the terminal boutons of the motor axon. The results suggest that the presynaptic neurotoxicity of snake venom phospholipases A(2) involves several components of the neuromuscular apparatus, including intracellular organelles of the motor nerve terminal.

New conopeptides of the D-superfamily selectively inhibiting neuronal nicotinic acetylcholine receptors.

The venom of cone snails (Conus spp.) is a rich source of peptides exhibiting a wide variety of biological activities. Several of these conopeptides are neuronal nicotinic acetylcholine receptor (nAChR) antagonists and belong to the A-, M-, S-, C and the recently described D-superfamily (alphaD-conopeptides). Here we describe the discovery and characterization of two alphaD-conopeptides isolated from the venom of Conus mustelinus and Conus capitaneus. Their primary structure was determined by Edman degradation, MS/MS analysis and by a PCR based approach. These peptides show close structural homology to the alphaD-VxXIIA, -B and -C conopeptides from the venom of Conus vexillum and are dimers (about 11kDa) of similar or identical peptides with 49 amino acid residues and a characteristic arrangement of ten conserved cysteine residues. These novel types of conopeptides specifically block neuronal nAChRs of the alpha7, alpha3beta2 and alpha4beta2 subtypes in nanomolar concentrations. Due to their high affinity, these new ligands may provide a tool to decipher the localisation and function of the various neuronal nAChRs.

High avidity anti-beta 2-glycoprotein I antibodies in patients with antiphospholipid syndrome.

OBJECTIVE: To evaluate avidity of IgG anti-beta 2-glycoprotein I antibodies (anti-beta2-GPI) in patients with antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE) in relation to thrombosis, and to demonstrate a possible affinity maturation of IgG anti-beta 2-GPI during the disease course. METHODS: 64 sera from 32 patients (18 with primary or secondary APS, 14 with SLE without APS) and their respective IgG fractions or affinity purified anti-beta 2-GPI were studied by anticardiolipin (aCL) and anti-beta 2-GPI enzyme linked immunosorbent assay and by chaotropic assay. RESULTS: Six, 12, and 14 patients had high, low, and heterogeneous avidity IgG anti-beta 2-GPI, respectively. In 12 patients an increase in antibody avidity was observed over a period of between four and 12 years. More patients with APS were in the high avidity than in the low avidity anti-beta 2-GPI group, while the opposite was observed for SLE alone (both p<0.05). The most common clinical feature among patients with high avidity anti-beta 2-GPI was thrombosis, mainly venous thrombosis (p<0.05 and p<0.02, respectively, v the low avidity anti-beta 2-GPI group). CONCLUSIONS: Patients with APS with or without SLE may have anti-beta2-GPI of high, low, or heterogeneous avidity. High avidity anti-beta 2-GPI appear to be associated with thrombosis and APS, while in pure SLE low avidity anti-beta 2-GPI may prevail. Monitoring of avidity may help elucidate the role of anti-beta 2-GPI affinity maturation in the pathogenesis of APS.

High-molecular-mass receptors for ammodytoxin in pig are tissue-specific isoforms of M-type phospholipase A(2) receptor.

Studying the molecular basis of presynaptic neurotoxicity of ammodytoxin C, a secretory phospholipase A(2) from the venom of Vipera a. ammodytes snake, we demonstrated the existence of two high-molecular-mass ammodytoxin C-binding proteins in porcine tissues, one in cerebral cortex and the other in liver. These proteins differ considerably in stability and Western blotting properties. However, as shown by immunological analysis and tandem mass spectrometry sequencing of several internal peptides derived from the purified receptors, both belong to secretory phospholipase A(2) receptors of the M type, which are Ca(2+)-dependent multilectins homologous to the macrophage mannose receptor. Based on Southern blot analysis of genomic DNA and deglycosylation of the receptors, the difference between the two proteins most likely stems from the different posttranscriptional and posttranslational modifications of a single gene product. Our findings raise the possibility that the M-type receptors for secretory phospholipases A(2) may display different physiological properties in different tissues.

A basic residue at position 36p of the propeptide is not essential for the correct folding and subsequent autocatalytic activation of prochymosin.

Position 36p in the propeptides of gastric aspartic proteinases is generally occupied by lysine or arginine. This has led to the conclusion that a basic residue at this position, which interacts with the active-site aspartates, is essential for folding and activation of the zymogen. Lamb prochymosin has been shown by cDNA cloning to possess glutamic acid at 36p. To investigate the effect of this natural mutation which appears to contradict the proposed role of this residue, calf and lamb prochymosins and their two reciprocal mutants, K36pE and E36pK, respectively, were expressed in Escherichia coli, refolded in vitro, and autoactivated at pH 2 and 4.7. All four zymogens could be activated to active chymosin and, at both pH values, the two proteins with Glu36p showed higher activation rates than the two Lys36p forms. Glu36p was also demonstrated in natural prochymosin isolated from the fourth stomach of lamb, as well as being encoded in the genomes of sheep, goat and mouflon, which belong to the subfamily Caprinae. A conserved basic residue at position 36p of prochymosin is thus not obligatory for its folding or autocatalytic activation. The apparently contradictory results for porcine pepsinogen A [Richter, C., Tanaka, T., Koseki, T. & Yada, R.Y. (1999) Eur. J. Biochem. 261, 746-752] can be reconciled with those for prochymosin. Lys/Arg36p is involved in stabilizing the propeptide-enzyme interaction, along with residues nearer the N-terminus of the propeptide, the sequence of which varies between species. The relative contribution of residue 36p to stability differs between pepsinogen and prochymosin, being larger in the former.

A high affinity acceptor for phospholipase A2 with neurotoxic activity is a calmodulin.

One of the high affinity binding proteins for ammodytoxin C, a snake venom presynaptically neurotoxic phospholipase A(2), has been purified from porcine cerebral cortex and characterized. After extraction from the membranes, the toxin-binding protein was isolated in a homogenous form using wheat germ lectin-Sepharose, Q-Sepharose, and ammodytoxin-CH-Sepharose chromatography. The specific binding of (125)I-ammodytoxin C to the isolated acceptor was inhibited to different extents by some neurotoxic phospholipases A(2), ammodytoxins, bee venom phospholipase A(2), agkistrodotoxin, and crotoxin; but not by nontoxic phospholipases A(2), ammodytin I(2), porcine pancreatic phospholipase A(2), and human type IIA phospholipase A(2); suggesting the significance of the acceptor in the mechanism of phospholipase A(2) neurotoxicity. The isolated acceptor was identified as calmodulin by tandem mass spectrometry. Since calmodulin is generally considered as an intracellular protein, the identity of this acceptor supports the view that secretory phospholipase A(2) neurotoxins have to be internalized to exert their toxic effect. Moreover, since ammodytoxin is known to block synaptic transmission, its interaction with calmodulin as an acceptor may constitute a valuable probe for further investigation of the role of the latter in this Ca(2+)-regulated process.

Neuronal receptors for phospholipases A(2 )and beta-neurotoxicity.

Some phospholipases A(2) interrupt neuromuscular communication by blocking the release of neurotransmitter into the synaptic cleft. Despite numerous studies, the molecular mechanism of their action is still largely obscure. In this review the best-characterized receptors for beta-neurotoxins are presented. We propose a model which could be useful in investigating the apparent inconsistency between the observed heterogeneity in the neuronal binding of beta-neurotoxins and the very similar pathomorphological and electrophysiological effects which they produce in the intoxicated tissue. We assume that beta-neurotoxins enter the nerve ending to exert their toxic effect. The model involves different pathways for phospholipase A(2) neurotoxins to reach the site of action inside the neuron, their respective extra- and intracellular neuronal receptors being key features of the pathway. Once in the nerve cell, beta-neurotoxins impair the function of the synaptic vesicles by phospholipid hydrolysis of the inner leaflet of the vesicle bilayer. The proportion of the products of the phospholipid hydrolysis, lysophospholipids and phospholipids in the membrane, has been demonstrated to be very important for the shaping of the membrane, affecting its fusogenic properties. Due to the same final step in the action of beta-neurotoxins, phospholipid hydrolysis, the consequences of their poisoning are practically identical.

Charge reversal of ammodytoxin A, a phospholipase A2-toxin, does not abolish its neurotoxicity.

The positive charge concentrated at the C-terminal region of ammodytoxin (Atx) A, which is involved in presynaptic toxicity, has been reversed. A six-site mutant of AtxA (K108N/K111N/K127T/K128E/E129T/K132E , where K108N=Lys(108)-->Asn etc. ) was prepared, in which five out of seven C-terminal basic amino acid residues were substituted with neutral or acidic ones. The mutant was approximately 30-fold less lethal, but still neurotoxic. Consistent with this, its binding affinity for the neuronal receptors decreased by only a factor of five. Additionally, a single-site mutant of AtxA was prepared, with substitution at only one position (K127T) out of six mutated in the six-site mutant. Its toxicity indicated that most, if not all, of the six mutated residues partially contribute to the decreased lethality of the multiple-site mutant.

The amino acid region 115-119 of ammodytoxins plays an important role in neurotoxicity.

Quadruple (Y115K/I116K/R118M/N119L) and double (Y115K/I116K) mutants of ammodytoxin A, a presynaptically toxic phospholipase A(2) from Vipera ammodytes ammodytes venom, were prepared and characterized. The enzymatic activity of the quadruple mutant on phosphatidylcholine micelles was threefold higher than that of AtxA, presumably due to higher phospholipid-binding affinity, whereas the activity of the double mutant was twofold lower. The substantial decrease by more than two orders of magnitude in the lethal potency of both mutants, together with their decreased binding affinity for neuronal receptors, indicates involvement of the amino acid region 115-119 in neurotoxicity. The similar decrease of toxicity for the two mutants points to the importance of the residues Y115 and I116.

Effects of ammodytin L on miniature and endplate potentials in neuromuscular junction of frog m. cutaneus pectoris.

Neurotoxic effects of ammodytin L (AtnL), a potent phospholipase A2 homologue, was studied in frog neuromuscular preparation m. cutaneous pectoris by measuring the influence of the toxin on the amplitude and the frequency of miniature and endplate potentials (MEPPs, EPPs). AtnL, in 100 nM concentration, significantly increases spontaneous quantal acetylcholine release from the motor nerve endings, observed as the increase in MEPPs frequency. At 100 nM or higher concentration the toxin decreases EPPs amplitude and the membrane potential (MP) simultaneously. No significant effect of AtnL on EPPs was observed at any concentration bellow 100 nM. Our results indicate that in frog AtnL shows the typical myotoxic effects, but it also exerts presynaptic effects.

Biochemical characterization of human cathepsin X revealed that the enzyme is an exopeptidase, acting as carboxymonopeptidase or carboxydipeptidase.

Cathepsin X, purified to homogeneity from human liver, is a single chain glycoprotein with a molecular mass of approximately 33 kDa and pI 5.1-5.3. Cathepsin X was inhibited by stefin A, cystatin C and chicken cystatin (Ki = 1.7-15.0 nM), but poorly or not at all by stefin B (Ki > 250 nM) and L-kininogen, respectively. The enzyme was also inhibited by two specific synthetic cathepsin B inhibitors, CA-074 and GFG-semicarbazone. Cathepsin X was similar to cathepsin B and found to be a carboxypeptidase with preference for a positively charged Arg in P1 position. Contrary to the preference of cathepsin B, cathepsin X normally acts as a carboxymonopeptidase. However, the preference for Arg in the P1 position is so strong that cathepsin X cleaves substrates with Arg in antepenultimate position, acting also as a carboxydipeptidase. A large hydrophobic residue such as Trp is preferred in the P1' position, although the enzyme cleaved all P1' residues investigated (Trp, Phe, Ala, Arg, Pro). Cathepsin X also cleaved substrates with amide-blocked C-terminal carboxyl group with rates similar to those of the unblocked substrates. In contrast, no endopeptidase activity of cathepsin X could be detected on a series of o-aminobenzoic acid-peptidyl-N-[2,-dinitrophenyl]ethylenediamine substrates. Furthermore, the standard cysteine protease methylcoumarine amide substrates (kcat/Km approximately 5.0 x 103 M-1.s-1) were degraded approximately 25-fold less efficiently than the carboxypeptidase substrates (kcat/Km approximately 120.0 x 103 M-1.s-1).

Tissue expression and immunolocalization of a novel human cathepsin P.

The mRNA of a novel human cathepsin P is expressed at high levels in lung, liver and heart. Using antibodies raised against recombinant cathepsin P produced in Escherichia coli, a single protein band of 33 kDa was detected by immunoblotting an extract of human liver. By immunofluorescence, positive signals were observed in hepatocytes and Kupffer cells of liver, and the distal tubule cells of kidney showing mainly perimembranous distribution, indicating a role, as yet unknown, for this novel putative protease that is distinct from other cathepsins of the papain family.

Partial primary structure of a fibrinogenase from the venom of the snake Lachesis stenophrys.

The partial primary structure of an Mr 24,000 non-haemorrhagic metalloproteinase isolated from the venom of the snake Lachesis stenophrys has been determined. The native proteinase was resistant to Edman degradation exhibiting the N-terminal blockade. The pyridylethylated or native proteinase was chemically and enzymatically fragmented and the obtained peptides were separated by gel or reversed-phase chromatography, and sequenced. The metalloproteinase from Lachesis stenophrys contains a putative zinc-chelating sequence HELGHNLGMKH, characteristic for the reprolysin family of zinc-metalloproteinases. It contains six cysteine residues in the standard positions for this group of proteins suggesting the same disulfide bonding. Interestingly, it has almost identical sequence as the metalloproteinase from Lachesis muta muta, LHF-II, which is, however, haemorrhagic. The main structural differences between the two molecules were found in their N-terminal parts and in glycosylation. As the substrate-binding regions of both proteinases are practically identical, we suggest that the absence of haemorrhagicity in Lachesis stenophrys enzyme is due to its lower affinity for the matrix proteins and not due to different substrate specificity.

Identification and purification of a novel receptor for secretory phospholipase A(2) in porcine cerebral cortex.

A specific phospholipase A(2) receptor from porcine cerebral cortex has been characterized (K(d) = 145 nM, B(max) = 0.4 pmol/mg membrane protein) by using a radioiodinated derivative of ammodytoxin C (AtxC), a snake venom presynaptically neurotoxic group IIA phospholipase A(2). After the receptor was solubilized in a ligand-binding form, it was approximately 14,000-fold enriched by chromatography on wheat germ lectin-Sepharose and AtxC-Affi-Gel 10. The receptor is a single chain glycoprotein with an apparent molecular mass of 180 kDa and binds toxic and non-toxic phospholipases A(2) of either group I or II. It also recognizes conjugates of bovine serum albumin with mannose, N-acetylglucosamine, and galactose. In its molecular mass and pharmacological profile, the AtxC receptor resembles the M-type receptor for secretory phospholipases A(2) from rabbit skeletal muscle (a C-type multilectin, homologous to macrophage mannose receptor), yet in terms of relative abundance in brain and antigenicity, these two receptors are completely different. A further AtxC receptor of approximately 200 kDa discovered in porcine liver was, however, recognized by anti-rabbit M-type phospholipase A(2) receptor antibodies. There are, therefore, two immunologically distinct secretory phospholipase A(2) receptors of about 200 kDa in the same species. Although the liver receptor is related to the M-type secretory phospholipase A(2) receptors, the brain receptor is not and belongs to a novel group of secretory phospholipase A(2) receptors.

Equinatoxins, pore-forming proteins from the sea anemone Actinia equina, belong to a multigene family.

The multigene family of equinatoxins, pore-forming proteins from sea anemone Actinia equina, has been studied at the protein and gene levels. We report the cDNA sequence of a new, sphingomyelin inhibited equinatoxin, EqtIV. The N-terminal sequences of natural Eqt I and III were also determined, confirming two isoforms of EqtI, differing at position 13. The number of Eqt genes determined by Southern blot hybridization was found to be more than five, indicating that Eqts belong to a multigene family.

An aromatic, but not a basic, residue is involved in the toxicity of group-II phospholipase A2 neurotoxins.

Ammodytoxins (Atxs) A, B and C are basic phospholipase A2s from Vipera ammodytes ammodytes snake venom, and they exhibit presynaptic toxicity. The most toxic is AtxA, followed by AtxC, its naturally occurring F124-->I/K128-->E mutant, which is 17 times less toxic. Two mutants of AtxA have been produced in bacteria and characterized. The specific enzymic activity of the K128-->E mutant on mixed phosphatidylcholine/Triton X-100 micelles is similar to that of the wild type. The K108-->N/K111-->N mutant, however, possesses 160% of the wild-type activity. Replacement of the two basic residues by uncharged, polar residues on the opposite side of the protein to the enzyme active site and interfacial adsorption surface results in increased enzymic activity at the water/lipid aggregate interface, due to a redistribution of electrostatic charge. The binding affinity of the double mutant for the specific acceptor in bovine brain was similar to that of AtxA, whereas the affinity of the single mutant was similar to that of AtxC, which was slightly weaker than that of AtxA. Interestingly, the substitution of any of these three basic surface residues did not significantly change the lethal potency of AtxA. Since the single mutant AtxA(K128-->E) is equivalent to the AtxC(I124-->F) mutant, this indicates that the residue at position 124 is important for presynaptic toxicity of Atxs. The more than 10-fold lower toxicity of AtxC, compared with AtxA, is a consequence of the substitution of Phe-124 (aromatic ring) with Ile (aliphatic chain). Exposed aromatic residues in the C-terminal region may also be important for the neurotoxicity of other similar toxins.