P-I class metalloproteinase from Bothrops moojeni venom is a post-proline cleaving peptidase with kininogenase activity: insights into substrate selectivity and kinetic behavior

Snake venom metalloproteinases (SVMPs) belonging to P-I class are able to hydrolyze extracellular matrix proteins and coagulation factors triggering local and systemic reactions by multiple molecular mechanisms that are not fully understood. BmooMPα-I, a P-I class SMVP from Bothrops moojeni venom, was active upon neuro- and vaso-active peptides including angiotensin I, bradykinin, neurotensin, oxytocin and substance P. Interestingly, BmooMPα-I showed a strong bias towards hydrolysis after proline residues, which is unusual for most of characterized peptidases. Moreover, the enzyme showed kininogenase activity similar to that observed in plasma and cells by kallikrein. FRET peptide assays indicated a relative promiscuity at its S2-S'2 subsites, with proline determining the scissile bond. This unusual post-proline cleaving activity was confirmed by the efficient hydrolysis of the synthetic combinatorial library MCA-GXXPXXQ-EDDnp, described as resistant for canonical peptidases, only after Pro residues. Structural analysis of the tripeptide LPL complexed with BmooMPα-I, generated by molecular dynamics simulations, assisted in defining the subsites and provided the structural basis for subsite preferences such as the restriction of basic residues at the S2 subsite due to repulsive electrostatic effects and the steric impediment for large aliphatic or aromatic side chains at the S1 subsite. These new functional and structural findings provided a further understanding of the molecular mechanisms governing the physiological effects of this important class of enzymes in envenomation process.

Batroxase, a new metalloproteinase from B. atrox snake venom with strong fibrinolytic activity

The structures and functional activities of metalloproteinases from snake venoms have been widely studied because of the importance of these molecules in envenomation. Batroxase, which is a metalloproteinase isolated from Bothrops atrox (Pará) snake venom, was obtained by gel filtration and anion exchange chromatography. The enzyme is a single protein chain composed of 202 amino acid residues with a molecular mass of 22.9 kDa, as determined by mass spectrometry analysis, showing an isoelectric point of 7.5. The primary sequence analysis indicates that the proteinase contains a zinc ligand motif (HELGHNLGISH) and a sequence C₁₆₄ I₁₆₅M₁₆₆ motif that is associated with a "Met-turn" structure. The protein lacks N-glycosylation sites and contains seven half cystine residues, six of which are conserved as pairs to form disulfide bridges. The three-dimensional structure of Batroxase was modeled based on the crystal structure of BmooMPα-I from Bothrops moojeni. The model revealed that the zinc binding site has a high structural similarity to the binding site of other metalloproteinases. Batroxase presented weak hemorrhagic activity, with a MHD of 10 μg, and was able to hydrolyze extracellular matrix components, such as type IV collagen and fibronectin. The toxin cleaves both α and β-chains of the fibrinogen molecule, and it can be inhibited by EDTA, EGTA and β-mercaptoethanol. Batroxase was able to dissolve fibrin clots independently of plasminogen activation. These results demonstrate that Batroxase is a zinc-dependent hemorrhagic metalloproteinase with fibrin(ogen)olytic and thrombolytic activity.

Low-molecular-mass peptides from the venom of the Amazonian viper Bothrops atrox protect against brain mitochondrial swelling in rat: potential for neuroprotection

The neurodegenerative diseases are important causes of morbidity and mortality in Western countries. Common mechanisms of toxicity involving mitochondrial damage have been suggested; however, a definitive treatment has not yet been found. Therefore, there has been great interest in the development of mitochondria-targeted protective compounds for the treatment of neuropathies. Animal toxins represent a promising source of new molecules with neuroprotective activity and potential to originate new drugs. We present here the effects of a low-molecular-mass peptides fraction (Ba-V) from Bothrops atrox snake venom, on rat brain mitochondrial function. Ba-V did not induce the mitochondrial swelling and moreover, was as effective as cyclosporin A (CsA) to inhibit the calcium/phosphate-induced swelling, which indicates its potential to prevent the mitochondrial permeability transition (MPT). The membrane electrochemical potential, the oxygen consumption during states-3 and -4 respirations as well as the respiratory control ratio (RCR) were not affected by Ba-V. Additionally, Ba-V did not induce reactive oxygen species (ROS) generation. Interestingly, Ba-V did not protect against the generation of ROS induced by t-BOH, which suggests a protection mechanism other than ROS scavenging. Given the important role of the mitochondrial damage and, more specifically, of MPT, in the development of neuropathies, Ba-V might be useful in the future strategies for the treatment of these diseases.

Structural studies of BmooMPalpha-I, a non-hemorrhagic metalloproteinase from Bothrops moojeni venom

Hemostatically active snake venom metalloproteinases (SVMPs) perturb the blood coagulation cascade at specific points and due to their potential application as thrombolytic agents, the fibrin(ogen)olytic non-hemorrhagic SVMPs have been employed as biochemical tools in coagulation research and diagnosis. Structural studies complemented by the design of metalloproteinase inhibitors have been instrumental in understanding their stereo specificity and action mechanism. We present here, details of the crystal structure of BmooMPalpha-I, a 22.6 kDa non-hemorrhagic P-I class SVMP isolated from Bothrops moojeni venom, determined at 1.76 A resolution. In this structure, the catalytic zinc ion displays an unusual octahedral coordination formed by the three canonical histidines (His(142), His(146) and His(152)) and additionally, by three solvent molecules. Comparative sequence and structural studies indicate that the motif comprising amino acid segments 153-164 and 167-176 adjacent to the methionine-turn is a salient feature that differentiates both non and hemorrhagic P-I class SVMPs and could directly be involved in the development of the hemorrhagic activity.

Functional and structural analysis of two fibrinogen-activating enzymes isolated from the venoms of Crotalus durissus terrificus and Crotalus durissus collilineatus

Fibrinogen-activating enzymes, widely distributed in Crotalidae and Viperidae venoms, are single-chain glycosylated serine proteases that display high macromolecular selectivity and are often referred to as thrombin-like enzymes (TLEs). TLEs serve as structural models to extend our understanding of the structure-function relationships of blood coagulation factors, have been clinically used for the treatment of thrombotic diseases, and are used as tools in clinical assays. The combination of gel filtration and ion-exchange chromatography proved to be successful in obtaining milligram quantities of pure samples of TLEs from the venoms of Crotalus durissus terrificus (white venom) and Crotalus durissus collilineatus (yellow venom). Functional characterization indicates that both enzymes preferentially degrade the Bb chain of bovine fibrinogen and possess edema-inducing and coagulant activities. However, the TLE from C. d. collilineatus venom shows twofold higher coagulant activity with a minimum coagulant dose (MCD) of 0.6 microg/microl, whereas the enzyme isolated from C. d. terrificus indicated an MCD of 1.5 microg/microl. Molecular modeling of gyroxin and structural comparisons with other highly conserved snake venom serine proteases, underlines the key role played by the surface charge distribution and the double insertion in the 174-surface loop in macromolecular substrate recognition by TLEs.

Insights into metal ion binding in phospholipases A2: ultra high-resolution crystal structures of an acidic phospholipase A2 in the Ca2+ free and bound states

The electrophile Ca(2+) is an essential multifunctional co-factor in the phospholipase A(2) mediated hydrolysis of phospholipids. Crystal structures of an acidic phospholipase A(2) from the venom of Bothrops jararacussu have been determined both in the Ca(2+) free and bound states at 0.97 and 1.60 A resolutions, respectively. In the Ca(2+) bound state, the Ca(2+) ion is penta-coordinated by a distorted pyramidal cage of oxygen and nitrogen atoms that is significantly different to that observed in structures of other Group I/II phospholipases A(2). In the absence of Ca(2+), a water molecule occupies the position of the Ca(2+) ion and the side chain of Asp49 and the calcium-binding loop adopts a different conformation.

Inhibition of the myotoxic activity of Bothrops jararacussu venom and its two major myotoxins, BthTX-I and BthTX-II, by the aqueous extract of Tabernaemontana catharinensis A. DC. (Apocynaceae)

Partial neutralization of the myotoxic effect of Bothrops jararacussu venom (BV) and two of its myotoxins [bothropstoxin-I (BthTX-I), catalytically inactive, and II (BthTX-II), showing low PLA2 activity], by the lyophilized aqueous extract of Tabernaemontana catharinensis (AE), was studied in rat isolated soleus muscle preparations (in vitro) and through i.m. injection in the gastrocnemius muscle (in vivo) by determination of creatine kinase (CK) activity and histopathological analysis. Incubation of soleus muscle for 1 h with BV or toxins (20 microg/ml) plus AE (400 microg/ml) added immediately after BV, BthTX-I or BthTX-II reduced CK levels by 53%, 37% and 56%, respectively. The myonecrotic effects of BV (20 microg/ml) upon soleus muscle was reduced 24%, 35% and 36% when AE (400 microg/ml) was added 1 h after BV and CK was evaluated 30 min, 1 and 2 h later, respectively. For BthTX-I these values were 46%, 48% and 47%, while for BthTX-II no inhibitory effect was detected. Histological analysis of soleus muscle after incubation with AE (400 microg/ml, 1 h) did not reveal any change in muscle fibers, but severe necrosis induced by BV or toxins (20 microg/ml) was clearly in evidence, and decreased significantly when soleus muscle was protected by AE. This protection was also observed when AE was administered 1 h after BV or BthTX-I, but not after BthTX-II. AE did not inhibit the catalytic PLA2 activity of BthTX-II or BV and did not change the PAGE pattern of BV, BthTX-I or BthTX-II. In vivo assays were performed in 100-g rats and maximal CK release was attained at a dose of 100 microg of BV, 3 h after injection. AE was not effective when injected 20 s after BV or toxins. However, injecting BV or toxins (100 microg), which were pre-incubated with AE (2 mg) caused an inhibition of 57%, 59% and 51%, respectively, with zero time pre-incubation, but was less effective with 1 h pre-incubation. This plant represents a potential source of promising myotoxin inhibitors.

Signalling pathways regulating human neutrophil migration induced by secretory phospholipases A2

This study was designed to elucidate the signalling pathways by which secretory phospholipases A2 (sPLA2s) induce in vitro neutrophil migration. The cell migration assays were performed with Naja mocambique venom PLA2 (sPLA2 with high catalytic activity), bothropstoxin-I (sPLA2 devoid of catalytic activity) and platelet-activating factor (PAF), using a 48-well microchemotaxis chamber. Both the non-selective protein kinase inhibitor staurosporine (30-300 nM) and the selective protein kinase C (PKC) inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpyperazine (H7; 50-200 microM) as well as the Gi inactivator pertussis toxin (30-300 nM) caused a concentration-dependent inhibition of the neutrophil migration induced by either N. mocambique venom PLA2 (100 microg/ml) or bothropstoxin-I (100 microg/ml). Pertussis toxin nearly abolished PAF-induced migration, while staurosporine and H7 partly (but significantly) inhibited the chemotactic responses to PAF. The dual inhibitor of cytosolic PLA2 and Ca2+ -independent PLA2 (iPLA2), arachidonil-trifluoromethyl-ketone (ATK; 0.2-20 microM), or the specific iPLA2 inhibitor bromoenol lactone (1-30 microM) caused a concentration-dependent inhibition of the migration induced by either sPLA2s. At the maximal concentration used for each compound, the migration was almost suppressed. In contrast, both of these compounds caused only slight inhibitions of PAF-induced migration. No rise in intracellular Ca2+ was observed in neutrophil-stimulated sPLA2, as determined in cells preloaded with fura 2-AM. In the experimental condition used, pertussis toxin, staurosporine, H7, ATK or bromoenol lactone did not induce cytotoxic effects, according to MTT assay. Our results suggest that activation of an endogenous PLA2 through activation of GTP-binding protein and PKC is the main mechanism by which exogenous sPLA2s cause neutrophil migration.

Anticrotalic and antitumoral activities of gel filtration fractions of aqueous extract from Tabernaemontana catharinensis (Apocynaceae)

The high mortality caused by Crotalus durissus terrificus snake venom is mainly due to crotoxin, which acts on the neuromuscular junction inhibiting the mechanism mediating acetylcholine release, thus leading to motor and respiratory paralysis and subsequently to animal death. We recently demonstrated that the aqueous extract (AE) of Tabernaemontana catharinensis can inhibit the lethal activity of C. d. terrificus venom. Eight fractions, PI to PVIII, were obtained by gel filtration of the extract on Sephadex G-10, and assayed for lethality and cytotoxicity. Fraction PVII [2.0 mg/100 g rat/50 microl saline solution (ss)] injected intramuscularly (i.m.) 20 s after the venom (240 microg) or crotoxin (200 microg/50 microl ss) neutralized the lethal activity of 2 LD50 of both. Fractions PI, PVI and PVIII (5.0 mg/100 g rat/50 microl ss) presented potent antitumoral activity in vitro against cells from human breast carcinoma (SK-BR-3) after 24 h incubation, as measured by Mosmann colorimetric method. Fraction PVII contains 12-methoxy-4-methylvoachalotine as its major component. These results demonstrate that the antivenom and antitumoral activities of the AE of T. catharinensis are exerted by different substances present in fraction PVII and fractions PI, PVI and PVIII, respectively, whose characteristics are distinct in terms of staining and Rf when analyzed by thin layer chromatography. The results also show that a preliminary fractionation by Sephadex G-10 gel filtration is a good option as a first step for isolation of biologically active substances from T. catharinensis.

Isolation, characterization and biological activity of acidic phospholipase A2 isoforms from Bothrops jararacussu snake venom

Acidic phospholipase A(2) (PLA(2)) isoforms in snake venoms, particularly those from Bothrops jararacussu, have not been characterized. This article reports the isolation and partial biochemical, functional and structural characterization of four acidic PLA(2)s (designated SIIISPIIA, SIIISPIIB, SIIISPIIIA and SIIISPIIIB) from this venom. The single chain purified proteins contained 122 amino acid residues and seven disulfide bonds with approximate molecular masses of 15 kDa and isoelectric points of 5.3. The respective N-terminal sequences were: SIIISPIIA-SLWQFGKMIDYVMGEEGAKS; SIIISPIIB-SLWQFGKMIFYTGKNEPVLS; SIIISPIIIA-SLWQFGKMILYVMGGEGVKQ and SIIISPIIIB-SLWQFGKMIFYEMTGEGVL. Crystals of the acidic protein SIIISPIIB diffracted beyond 1.8 A resolution. These crystals are monoclinic with unit cell dimensions of a = 40.1 A, b = 54.2 A and c = 90.7 A. The crystal structure has been refined to a crystallographic residual of 16.1% (R(free) = 22.9%). Specific catalytic activity (U/mg) of the isolated acidic PLA(2)s were SIIISPIIA = 290.3 U/mg; SIIISPIIB = 279.0 U/mg; SIIISPIIIA = 270.7 U/mg and SIIISPIIIB = 96.5 U/mg. Although their myotoxic activity was low, SIIISPIIA, SIIISPIIB and SIIISPIIIA showed significant anticoagulant activity. However, there was no indirect hemolytic activity. SIIISPIIIB revealed no anticoagulant, but presented indirect hemolytic activity. With the exception of SIIISPIIB, which inhibited platelet aggregation, all the others were capable of inducing time-independent edema. Chemical modification with 4-bromophenacyl bromide did not inhibit the induction of edema, but did suppress other activities.

Crystal structure of the platelet activator convulxin, a disulfide-linked α4β4 cyclic tetramer from the venom of Crotalus durissus terrificus

Convulxin (CVX), a C-type lectin, isolated from the venom of the South American rattlesnake Crotalus durissus terrificus, causes cardiovascular and respiratory disturbances and is a potent platelet activator which binds to platelet glycoprotein GPVI. The structure of CVX has been solved at 2.4A resolution to a crystallographic residual of 18.6% (R(free)=26.4%). CVX is a disulfide linked heterodimer consisting of homologous alpha and beta chains. The heterodimers are additionally linked by disulfide bridges to form cyclic alpha(4)beta(4)heterotetramers. These domains exhibit significant homology to the carbohydrate-binding domains of C-type lectins, to the factor IX-binding protein (IX-bp), and to flavocetin-A (Fl-A) but sequence and structural differences are observed in both the domains in the putative Ca(2+)and carbohydrate binding regions.

Initial structural analysis of an α4β4C-type lectin from the venom ofCrotalus durissus terrificus

Convulxin, an alphabeta C-type lectin, is a potent platelet activator isolated from the venom of the South American rattlesnake Crotalus durissus terrificus. It is a 26.5 kDa alphabeta heterodimer consisting of two homologous disulfide-linked chains. The crystals belong to space group I4, with unit-cell parameters a = b = 131.61, c = 121.85 A, and diffraction data were collected to 2.7 A. The structure was solved by molecular replacement and the asymmetric unit contains two alphabeta heterodimers, each of which forms a disulfide-linked cyclic alpha(4)beta(4) tetramer in the unit cell. These alpha(4)beta(4) tetramers are stacked to form a large solvent channel.

Mn(2+) ions reduce the enzymatic and pharmacological activities of bothropstoxin-I, a myotoxic Lys49 phospholipase A(2) homologue from Bothrops jararacussu snake venom

Bothropstoxin-I (BthTX-I), a myotoxic Lys49 phospholipase A(2) (PLA(2)) homologue isolated from Bothrops jararacussu snake venom, causes a range of biological effects, including myonecrosis, mouse paw edema, irreversible neuromuscular blockade and lysis of cell cultures. Among eight divalent cations assayed, Mn(2+) was the most effective in reducing mouse paw edema induced by BthTX-I (25 microg). Preincubating BthTX-I with Mn(2+) (1.0mM) reduced mouse paw edema by 70% and myotoxicity by 60% in mice injected i.m. with 50 microg toxin. Mn(2+) (50 microl of a 1mM solution) administered within 1min at the site of toxin injection was still but less effective in antagonising BthTX-I-induced myotoxicity. Mn(2+) (1.0mM) completely prevented BthTX-I (1.4 microM)-induced neuromuscular blockade in the mouse phrenic-nerve diaphragm preparation. Mn(2+) (0.25mM) protected about 85% of NB41A3 cells from lysis when coincubated with BthTX-I (1.0 microM) for 25h. Preincubation with 0.25mM Mn(2+) increased the sensitivity of the cells to subsequent lysis by BthTX-I in the absence of Mn(2+). BthTX-I (1 microM) caused extensive fatty acid release (from 0.8% of the total radiolabeled lipid in control cells to 56% with toxin) when incubated with the NB41A3 cell line for 25h. PLA(2) activity observed in cell cultures after addition of BthTX-I was considerably reduced by 0.25mM Mn(2+). Mn(2+) ions constitute a promising agent to assess the action mechanism and the effects of enzymatic inhibition on the pharmacological activity of Lys49 PLA(2) homologues.