Isolation and pharmacological characterization of a new cytotoxic L-amino acid oxidase from Bungarus multicinctus snake venom.

ETHNOPHARMACOLOGICAL RELEVANCE: Bungarus multicinctus snake belongs to Elapidae family and is widely distributed in southern China. It is widely used in traditional Chinese medicine with the effect of dispelling wind and removing obstruction in the meridians. Moreover, it is also as a chief ingredient of many polyherbal formulations for the treatment of cancer. AIM OF THE STUDY: To evaluate the antitumor activity of Bungarus multicinctus snake venom components and isolate, characterize the most effective anti-tumor component of Bungarus multicinctus snake venom. MATERIALS AND METHODS: The in vitro antitumor activity of Bungarus multicinctus venom components was detected by cytotoxicity assay and cell apoptosis assay. A unique LAAO from Bungarus multicinctus venom named as BM-Apotxin was isolated and characterized by Sephadex G-75 gel filtration, Sephadex G-25 desalting, Q ion-exchange chromatography and subsequent amino acids sequence determination. The LAAO activity and enzyme kinetics of BM-Apotxin was detected by microplate assay. RESULTS: BM-Apotxin, a 65KDa glycoprotein, which contributed to the most anti-tumor effects of Bungarus multicinctus venom. BM-Apotxin can selectively kill tumor cells, with less cytotoxicity to the normal cells. BM-Apotxin is an L-amino acid oxidase (LAAO) with high sequence identity to other snake venom LAAOs. Its anti-tumor activity is mainly due to the hydrogen peroxide produced from LAAO oxidation. But the catalase did not reverse its anti-tumor effect completely. Like other snake venom LAAOs, BM-Apotxin can oxidize many L amino acids, not D amino acids. The optimum substrate for BM-Apotxin is L-Phe. Moreover, BM-Apotxin deglycosylation can significantly reduce the LAAO activity and anti-tumor activity of BM-Apotxin. CONCLUSION: This study will facilitate the study on anti-tumor mechanism of snake venom and drug development based on Bungarus multicinctus venom.

Cytotoxic activity of NN-32 toxin from Indian spectacled cobra venom on human breast cancer cell lines.

BACKGROUND: Breast cancer is the most common cancer which causes significant morbidity and mortality among women worldwide. Lack of medical facilities for early detection, therapeutic strategies for treatment and side effects due to pharmacological compounds have encompassed the need for new therapies mostly from natural sources. A lot of components have been identified from different snake venoms as therapeutic agents. A group of polypeptides (60-70 amino acid residues) called cytotoxins or cardiotoxins present in an elapid family of snakes have a wide variety of pharmaceutical actions and have the tendency to damage a wide variety of cells including cancerous cells. The aim of the present study was to evaluate the cytotoxic effect of NN-32 protein toxin purified from Indian Spectacled Cobra venom against human breast cancer cell lines (MCF-7 and MDA-MB-231). METHODS: The NN-32 toxin was purified by ion exchange chromatography and further by RP-HPLC. The potential anticancer effects of the NN-32 toxin on MCF-7 and MDA-MB-231 cells were evaluated using MTT, anti-proliferation, neutral red (NR) uptake and Lactate Dehydrogenase (LDH) release assay. RESULTS: The ion exchange chromatography showed various peaks among fraction no. 35 showing cytotoxic activity and this fraction showed a single peak with retention time 3.6 mins by HPLC using C18 column. The NN-32 toxin induced cytotoxicity in MCF-7 and MDA-MB-231 cells with the IC50 value of 2.5 and 6.7 µg/ml respectively. The NN-32 showed significant cytotoxicity to both the cell lines along with low cytotoxicity to MCF-10A (normal breast epithelial) cells. The cytotoxic effect was further confirmed by the anti-proliferative, NR uptake and LDH release assays. CONCLUSION: The purified toxin NN-32 from Naja naja venom showed cytotoxic activity against MCF-7 (ER+) and MDA-MB-231(ER-) cells in both dose dependent and time dependent manner.

Cobrotoxin extracted from Naja atra venom relieves arthritis symptoms through anti-inflammation and immunosuppression effects in rat arthritis model.

ETHNOPHARMACOLOGICAL RELEVANCE: The Naja atra (Chinese cobra), primarily distributing in the low or medium altitude areas of southern China and Taiwan, was considered as a medicine in traditional Chinese medicine and used to treat pain, inflammation and arthritis. AIM OF THE STUDY: To study the anti-inflammatory and anti-arthritic activities of cobrotoxin (CTX), an active component of the venom from Naja atra. MATERIALS AND METHODS: Adjuvant-induced arthritis (AA) rats were used as the animal model of rheumatoid arthritis. The anti-arthritic effects of CTX were evaluated through the arthritis score, paw edema and histopathology changes of joints. The anti-inflammation effects were assayed by the level of IL-6, TNF-α, IL-1ß and the number of inflammatory cells in peripheral blood, as well as the proliferation of fibroblast-like synoviocytes (FLS). The immune level was valued by the proliferation of T cells and the level of CD4 and CD8. RESULTS: CTX alleviated the disease development of AA rats according to the ameliorating arthritis score, paw edema and histopathology character. At the meanwhile, CTX decreased the levels of IL-6, TNF-α, IL-1ß and the numbers of inflammatory cells in peripheral blood. CTX also suppressed the abnormal increasing of CD4+ T cells/ CD8+ T cells ratio, and could significantly inhibit T cell proliferation. Consistent with its effects on inhibiting granuloma's formation, CTX inhibited the proliferation of the cultured FLSs. Further studies on inflammatory signaling in FLSs revealed that CTX could inhibit the NF-κB signaling pathway. CONCLUSIONS: CTX has beneficial effects on rheumatoid arthritis by its immune regulation effects and anti-inflammation effects. The inhibition of NF-κB pathway partly contributes to the anti-inflammatory properties of CTX.

Screening of an anti-inflammatory peptide from Hydrophis cyanocinctus and analysis of its activities and mechanism in DSS-induced acute colitis.

Snake has been used for centuries as a traditional Chinese medicine, especially for therapeutic treatment for inflammatory diseases; however, its mechanisms of action and active constituents remain controversial. In our study, a tumor necrosis factor receptor 1 (TNFR1) selective binding peptide, Hydrostatin-SN1 (H-SN1), which was screened from a Hydrophis cyanocinctus venom gland T7 phage display library, was shown to exhibit significant anti-inflammatory activity in vitro and in vivo. As a TNFR1 antagonist, it reduced cytotoxicity mediated by TNF-α in L929 fibroblasts and effectively inhibited the combination between TNF-α with TNFR1 in surface plasmon resonance analysis. H-SN1 was also shown to suppress TNFR1-associated signaling pathways as it minimized TNF-α-induced NF-кB and MAPK activation in HEK293 embryonic kidney and HT29 adenocarcinoma cell lines. We next determined the effect of H-SN1 in vivo using a murine model of acute colitis induced by dextran sodium sulfate, demonstrating that H-SN1 lowered the clinical parameters of acute colitis including the disease activity index and histologic scores. H-SN1 also inhibited TNF/TNFR1 downstream targets at both mRNA and protein levels. These results indicate that H-SN1 might represent a suitable candidate for use in the treatment of TNF-α-associated inflammatory diseases such as inflammatory bowel diseases.

Humanized cobra venom factor: structure, activity, and therapeutic efficacy in preclinical disease models.

The complement system is an integral component of both innate and adaptive immunity. However, complement is also a pathogenetic factor in many diseases. The development of agents for therapeutic complement inhibition is the topic of intense investigations by many investigators. We have developed a distinctly different therapeutic approach: complement depletion rather than inhibition. This approach is based on cobra venom factor (CVF), a C3 analog known to be able to safely deplete complement. This manuscript will briefly review the structure and activity of CVF, along with its similarities and differences to C3. Exploiting the knowledge of the structure/function relationship of CVF and C3, we created derivatives of human C3 which display the CVF-like activity of depleting complement, referred to as humanized CVF (hCVF). This review describes the structure and activity of hCVF, including the important property of not cleaving C5. The efficacy of hCVF for therapeutic complement depletion in nine preclinical models diseases with complement pathology is reviewed, including reperfusion injury, age-related macular degeneration (AMD), paroxysmal nocturnal hemoglobinuria (PNH), and immunogenicity of Factor VIII in hemophilia A. Complement depletion is characterized by the absence of toxicity, even after intra-arterial injection into the pulmonary artery of primates. No immunogenicity has been observed.

The anticancer effect of cytotoxin 1 from Naja atra Cantor venom is mediated by a lysosomal cell death pathway involving lysosomal membrane permeabilization and cathepsin B release.

The cytotoxin family of cobra venom proteins, also called cardiotoxins, can activate both necrotic and apoptotic cell death pathways in cancer cells. Cytotoxin 1 (CTX1)from Naja atra Cantor venom is a 60 amino acid, 6698 Da protein with as yet untested anticancer efficacy and cell selectivity. We tested the toxicity of CTX1 on a number of cancer cell lines (MCF-7, P388, K562, and H22) and on one normal human cell line (16HBE). The rank order of cytotoxicity was MCF-7 > P388 ≈ K562 >H22 ≈ 16HBE, indicating that the effect of CTX1 on certain cancer cell types was relatively selective.Treatment with CTX1 greatly prolonged the survival of P388 ascites tumors bearing KM mice compared to cyclophosphamide treatment. Cell viability, apoptosis, and lysosomal permeability assays all demonstrated that CTX1 induced dose- and time-dependent cell death, with most cells exhibiting the morphological and biochemical features of late apoptosis and necrosis. Mitochondrial membrane potential was lost in CTX1-treated P388 cells. In addition, CTX1 induced an increase in both lysosomal membrane permeability and cathepsin B protease activity. These analyses reveal that CTX1 possesses significant and selective anticancer activity, likely by inducing programmed cell death through mitochondrial and/or lysosomal pathways.

Anti-inflammatory effects of Neurotoxin-Nna, a peptide separated from the venom of Naja naja atra.

BACKGROUND: Neurotoxin-Nna (NT), an analgesic peptide separated from the venom of Naja naja atra, has reported to have an exceptional specificity to block transmission of the nerve impulse by binding to the α- subunit of the nicotinic acetylcholine receptor in the membrane. However, little information is available on the anti-inflammatory effects of NT. Therefore, the anti-inflammatory activity of Neurotoxin-Nna was investigated in this study. METHODS: The anti-inflammatory effects of NT were evaluated by measuring its influence on several crucial factors in inflammatory pathways, including total antioxidant activity, antinociceptive effects in vivo, nuclear factor kappa B (NF-κB), polymorphonuclear cells (PMN), inducible nitric oxide synthase (iNOS), adhesion molecule (ICAM-1) and tactile hyperalgesia. RESULTS: NT treatment decreased the levels of tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1ß). NT treatment decreased the total antioxidant status (TAOS) and reduced CFA-induced tactile hyperalgesia in a dose-dependent manner. NT significantly inhibited regulation of NF-kappaB activation and the production of IL-1ß, TNF-α, iNOS and CAM-1. Moreover, NT suppressed infiltration of PMN. CONCLUSIONS: Our results showed that NT reduced CFA-induced tactile hyperalgesia through inhibition inflammatory pathways in experimental inflammatory rats.

[Isolation and pharmacological properties of analgesic fraction from venom of Naja Naja atra].

OBJECTIVE: To separate main analgesic fraction from venom of Guangdong Naja naja atra, to establish the basis for the using of Naja naja atra and find new analgesic fraction. METHODS: Affinity chromatography and size exclusion were used to isolate the analgesic fraction from the venom of Naja naja atra, and then to determine its properties by biochemical methods, such as SDS-polyacryamide gel electrophoresis ( SDS-PAGE), HPLC and Mole-toff. RESULTS: HPLC showed its relative purity was 95% (HPLC)and Mw was 6741. 236 Da. We observed that peripheral administration of neurotoxin strongly reduced the mechanical allogynia and thermal hyperalgesia for 24 hours, associated with this neuropathy (L5 spinal nerve ligation). CONCLUSION: The fraction from venom of Naja naja atra has significant analgesic effect and it is worth further developing.

Molecular docking studies and anti-snake venom metalloproteinase activity of Thai mango seed kernel extract.

Snakebite envenomations cause severe local tissue necrosis and the venom metalloproteinases are thought to be the key toxins involved. In this study, the ethanolic extract from seed kernels of Thai mango (Mangifera indica L. cv. 'Fahlun') (Anacardiaceae) and its major phenolic principle (pentagalloylglucopyranose) exhibited potent and dose-dependent inhibitory effects on the caseinolytic and fibrinogenolytic activities of Malayan pit viper and Thai cobra venoms in in vitro tests. molecular docking studies revealed that the binding orientations of the phenolic principles were in the binding pockets of snake venom metalloproteinases (SVMPs). The phenolic principles could form hydrogen bonds with the three histidine residues in the conserved zinc-binding motif and could chelate the Zn(2+) atom of the SVMPs, which could potentially result in inhibition of the venom enzymatic activities and thereby inhibit tissue necrosis.

Isolation of a snake venom phospholipase A2 (PLA2) inhibitor (AIPLAI) from leaves of Azadirachta indica (Neem): mechanism of PLA2 inhibition by AIPLAI in vitro condition.

A compound (AIPLAI (Azadirachta indica PLA(2) inhibitor)) purified from the methanolic leaf extract of A. indica (Neem) inhibits the cobra and Russell's viper venoms (RVVs) phospholipase A(2) enzymes in a dose-dependent manner. Inhibition of catalytic and tested pharmacological properties of cobra venom (Naja naja and Naja kaouthia) PLA(2) enzymes by AIPLAI is significantly higher (P<0.05) compared to the inhibition of PLA(2) enzymes of crude RVV (Daboia russelli) when tested under the same condition. Kinetic study reveals that in in vitro condition, AIPLAI inhibits the purified N. kaouthia PLA(2) enzymes in a non-competitive manner. The AIPLAI is quite stable at room temperature. The present study shows that AIPLAI holds good promise for the development of novel anti-snake venom drug in future.

A model study of interactions between TcAChE peripheral site segment Tyr70Val71 and loop 1 of Fasciculin 2.

The continuous chain of residues (Thr7 to Ala12) of Loop1 of Fas2 (F1) and its interaction with the peripheral binding sites (Tyr70-Val71) of AChE (P1) has been studied. Our results suggest that the flexibility of Loop1 might be caused by either the partially protonated guanidine group of Arg11 under experimental conditions or by the interaction with the negatively charged center of substrates. The binding energy of F1-P1 is predicted to be -16.6 kcal/mol at the B3LYP/6-311G(d,p) level, which is assumed to originate from one isolated O7...HN10 H-bond, one possible O10...HC71 unconventional O...HC type H-bonding, and the improved pi-bonding cooperativity around the peptide group of the AChE segment Tyr70-Val71. The classical Kitaura-Morokuma energy decomposition analysis, the NPA charge analysis, and the AIM analysis consistently reveal that the peptide group in segment P1 is more polarizable, which might play the key role in the interactions between F1 and P1. The PCM solvent effect corrected results reveal decrease of the interaction energy of the considered model. The importance of Thr8 of Fas2 in the P-site binding of AChE is also concluded. Site-directed mutations on either the Fas2 residue of Thr8 or the AChE residue of Tyr70 are expected to alter the binding behavior of the Loop1 of Fas2 with AChE.

Fully oxidized scrambled isomers are essential and predominant folding intermediates of cardiotoxin-III.

Scrambled isomers (X-isomers) are fully oxidized, non-native isomers of disulfide proteins. They have been shown to represent important intermediates along the pathway of oxidative folding of numerous disulfide proteins. A simple method to assess whether X-isomers present as folding intermediate is to conduct oxidative folding of fully reduced protein in the alkaline buffer alone without any supplementing thiol catalyst or redox agent. Cardiotoxin-III (CTX-III) contains 60 amino acids and four disulfide bonds. The mechanism of oxidative folding of CTX-III has been systematically characterized here by analysis of the acid trapped folding intermediates. Folding of CTX-III was shown to proceed sequentially through 1-disulfide, 2-disulfide, 3-disulfide and 4-disulfide (scrambled) isomers as folding intermediates to reach the native structure. When folding of CTX-III was performed in the buffer alone, more than 97% of the protein was trapped as 4-disulfide X-isomers, unable to convert to the native structure due to the absence of thiol catalyst. In the presence of thiol catalyst (GSH) or redox agents (GSH/GSSG), the recovery of native CTX-III was 80-85%. These results demonstrate that X-isomers play an essential and predominant role in the oxidative folding of CTX-III.

Crystal structure of a heterodimer of phospholipase A2 from Naja naja sagittifera at 2.3 A resolution reveals the presence of a new PLA2-like protein with a novel cys 32-Cys 49 disulphide bridge with a bound sugar at the substrate-binding site.

The crystal structure of the phospholipase A2 (PLA2) heterodimer from Naja naja sagittifera reveals the presence of a new PLA2-like protein with eight disulphide bridges. The heterodimer is formed between a commonly observed group I PLA2 having seven characteristic disulfide bonds and a novel PLA2-like protein (Cys-PLA2) containing two extra cysteines at two highly conserved sites (positions 32 and 49) of structural and functional importance. The crystals of the heterodimer belong to tetragonal space group P41212 with cell dimensions, a = b = 77.7 A and c = 68.4 A corresponding to a solvent content of 33%, which is one of the lowest values observed so far in the PLA2 crystals. The structure has been solved with molecular replacement method and refined to a final R value of 21.6% [Rfree = 25.6%]. The electron density revealed the presence of cysteines 32 and 49 that are covalently linked to give rise to an eighth disulphide bridge in the PLA2-like monomer. A non-protein high-quality electron density was also observed at the substrate-binding site in the PLA2-like protein that has been interpreted as N-acetylglucosamine. The overall tertiary folds of the two monomers are similar having all features of PLA2-type folding. A zinc ion is detected at the interface of the heterodimer with fivefold coordination while another zinc ion was found on the surface of Cys-PLA2 with sixfold coordination. The conformations of the calcium-binding loops of both monomers are significantly different from each other as well as from those in other group I PLA2s. The N-acetylglucosamine molecule is favorably placed in the substrate-binding site of Cys-PLA2 and forms five hydrogen bonds and several van der Waals interactions with protein atoms, thus indicating a strong affinity. It also provides clue of the possible mechanism of sugar recognition by PLA2 and PLA2-like proteins. The formation of heterodimer seems to have been induced by zinc ion.

Strong myotoxic activity of Trimeresurus malabaricus venom: role of metalloproteases.

Trimeresurus malabaricus is an endemic snake found in the Southern region of Western Ghats section of India along with the more widely distributed species like Naja naja and Daboia russelii. T. malabaricus venom is not lethal when injected (i.p.) up to 20 mg/kg body weight in mice, but causes extensive local tissue degeneration. N. naja and D. russelii are highly toxic (i.p.) with minimum local tissue damage in experimental mice. In this study a comparative analysis of local tissue damage of T. malabaricus venom is made with N. naja and D. russelii snake venoms of the Southern regions of Western Ghats. T. malabaricus venom exhibits caseinolytic activity 16 and 24 times more than N. naja and D. russelii venom. Inhibition studies with specific protease inhibitors reveal that the major proteases belong to metalloproteases. T. malabaricus venom hydrolyses gelatin and induces strong hemorrhagic activity in mice. Both N. naja and D. russelii fail to hydrolyze gelatin even at very high concentration and did not induce any hemorrhagic activity. With D. russelii venom small hemorrhagic spot was observed at the site of injection. The hemorrhagic activity of T. malabaricus venom is completely neutralized by metalloprotease inhibitors and not by serine protease inhibitor. The i.m. injection of T. malabaricus venom causes extensive degradation of muscle tissue within 24 h. The light microscopic observation of muscle tissue showed congestion of blood vessels and hemorrhage at the early stage followed by extensive necrosis of muscle fibers. The elevated levels of serum CK and LDH activity further supported the muscle degeneration. Such pathological symptoms were not seen with N. naja and D. russelii snake venom. The hemorrhagic and the muscle necrosis was completely neutralized by metalloprotease inhibitors and not by serine protease inhibitor strongly suggests that the major toxin component in the T. malabaricus venom is metalloprotease and its activity can be easily neutralized using chelating agents and its use in the first aid as chelation therapy is beneficial.

Comparative analysis of prothrombin activators from the venom of Australian elapids.

A key component of the venom of many Australian snakes belonging to the elapid family is a toxin that is structurally and functionally similar to that of the mammalian prothrombinase complex. In mammals, this complex is responsible for the cleavage of prothrombin to thrombin and is composed of factor Xa in association with its cofactors calcium, phospholipids, and factor Va. The snake prothrombin activators have been classified on the basis of their requirement for cofactors for activity. The two major subgroups described in Australian elapid snakes, groups C and D, are differentiated by their requirement for mammalian coagulation factor Va. In this study, we describe the cloning, characterization, and comparative analysis of the factor X- and factor V-like components of the prothrombin activators from the venom glands of snakes possessing either group C or D prothrombin activators. The overall domain arrangement in these proteins was highly conserved between all elapids and with the corresponding mammalian clotting factors. The deduced protein sequence for the factor X-like protease precursor, identified in elapids containing either group C or D prothrombin activators, demonstrated a remarkable degree of relatedness to each other (80%-97%). The factor V-like component of the prothrombin activator, present only in snakes containing group C complexes, also showed a very high degree of homology (96%-98%). Expression of both the factor X- and factor V-like proteins determined by immunoblotting provided an additional means of separating these two groups at the molecular level. The molecular phylogenetic analysis described here represents a new approach for distinguishing group C and D snake prothrombin activators and correlates well with previous classifications.

Structure and function of recombinant cobra venom factor.

Cobra venom factor (CVF) is the complement-activating protein from cobra venom. It is a structural and functional analog of complement component C3. CVF functionally resembles C3b, the activated form of C3. Like C3b, CVF binds factor B, which is subsequently cleaved by factor D to form the bimolecular complex CVF,Bb. CVF,Bb is a C3/C5 convertase that cleaves both complement components C3 and C5. CVF is a three-chain protein that structurally resembles the C3b degradation product C3c, which is unable to form a C3/C5 convertase. Both C3 and CVF are synthesized as single-chain prepro-proteins. This study reports the recombinant expression of pro-CVF in two insect cell expression systems (baculovirus-infected Sf9 Spodoptera frugiperda cells and stably transfected S2 Drosophila melanogaster cells). In both expression systems pro-CVF is synthesized initially as a single-chain pro-CVF molecule that is subsequently proteolytically processed into a two-chain form of pro-CVF that structurally resembles C3. The C3-like form of pro-CVF can be further proteolytically processed into another two-chain form of pro-CVF that structurally resembles C3b. Unexpectedly, all three forms of pro-CVF exhibit functional activity of mature, natural CVF. Recombinant pro-CVF supports the activation of factor B in the presence of factor D and Mg2+ and depletes serum complement activity like natural CVF. The bimolecular convertase pro-CVF,Bb exhibits both C3 cleaving and C5 cleaving activity. The activity of pro-CVF and the resulting C3/C5 convertase is indistinguishable from CVF and the CVF,Bb convertase. The ability to produce active forms of pro-CVF recombinantly ensures the continued availability of an important research reagent for complement depletion because cobra venom as the source for natural CVF will be increasingly difficult to obtain as the Indian cobra is on the list of endangered species. Experimental systems to express pro-CVF recombinantly will also be invaluable for studies to delineate the structure and function relationship of CVF and its differences from C3 as well as to generate human C3 derivatives with CVF-like function for therapeutic complement depletion ("humanized CVF").

A synthetic weak neurotoxin binds with low affinity to Torpedo and chicken alpha7 nicotinic acetylcholine receptors.

Weak neurotoxins from snake venom are small proteins with five disulfide bonds, which have been shown to be poor binders of nicotinic acetylcholine receptors. We report on the cloning and sequencing of four cDNAs encoding weak neurotoxins from Naja sputatrix venom glands. The protein encoded by one of them, Wntx-5, has been synthesized by solid-phase synthesis and characterized. The physicochemical properties of the synthetic toxin (sWntx-5) agree with those anticipated for the natural toxin. We show that this toxin interacts with relatively low affinity (K(d) = 180 nm) with the muscular-type acetylcholine receptor of the electric organ of T. marmorata, and with an even weaker affinity (90 microm) with the neuronal alpha7 receptor of chicken. Electrophysiological recordings using isolated mouse hemidiaphragm and frog cutaneous pectoris nerve-muscle preparations revealed no blocking activity of sWntx-5 at microm concentrations. Our data confirm previous observations that natural weak neurotoxins from cobras have poor affinity for nicotinic acetylcholine receptors.

Site-directed mutagenesis of m1-toxin1: two amino acids responsible for stable toxin binding to M(1) muscarinic receptors.

m1-Toxin1 binds specifically and irreversibly to M(1) muscarinic receptors and can slow the dissociation of [(3)H]N-methylscopolamine ([(3)H]NMS) from these receptors. Yet only 7 of its 65 amino acids are not conserved in six other mamba toxins that bind reversibly to M(2)-M(5) muscarinic receptors. Two of these seven residues (Phe(38), Lys(65)) were mutated to corresponding residues of the other toxins (Ile(38), Glu(65)), to evaluate amino acids in m1-toxin1 that confer its remarkable affinity and specificity. The cDNA for m1-toxin1 was cloned from venom gland mRNA using polymerase chain reaction (PCR)-based techniques. Its nucleotide sequence is remarkably similar to those of other short-chain neurotoxins. The cDNAs for mutant toxins Phe(38) to Ile(38) (F38I) and Lys(65) to Glu(65) (K65E) were constructed by PCR-based techniques. Each cDNA was expressed in yeast, and the toxins were purified from yeast media by cation-exchange and reversed phase chromatography. Recoveries were 40 to 152 microg/l. Recombinant m1-toxin1 was identical to the native toxin (observed mass: 7471 Da; irreversible blockade of [(3)H]NMS binding to cloned M(1) receptors at 25 degrees C; no blockade of M(2)-M(5) receptors; 6-fold slowing of [(3)H]NMS dissociation at 37 degrees C). F38I also bound specifically to M(1) receptors, but reversibly and without effect on NMS dissociation. Thus, Phe(38) contributes to the stability of toxin-receptor complexes, but not to M(1)-selectivity. K65E bound selectively and irreversibly to unliganded M(1) receptors but did not slow NMS dissociation. It is suggested that the C-terminal Lys(65) of m1-toxin1 may contact an outer loop of the M(1) receptor.

Snake bite in Nigeria.

Four families of venomous snakes are found in Nigeria--Viperidae, Elapidae, Colubridae and Actraspididae but three species carpet viper (Echis ocellatus), black-necked spitting cobra (Naja nigricollis) and puff adder (Bitis arietans), belonging to the first two families, are the most important snakes associated with envenoming in Nigeria. The incidence of bites has been reported as 497 per 100,000 population per year with a 12 percent natural mortality, with Echis ocellatus accounting for at least 66 percent in certain foci. Bites occur more often while victims were farming, herding or walking although the spitting cobra may bite victims who roll upon it in their sleep. Carpet viper venom contains a prothrombin activating procoagulant, haemorrhagin and cytolytic fractions which cause haemorrhage, incoagulable blood, shock and local reactions/ necrosis. The spitting cobra bite manifests with local tissue reaction and occassionally with bleeding from the site of bite, but no classic neurotoxic feature has been observed except following Egyptian cobra (N. haje) bites. Cardiotoxicity and renal failure may occassionally occur following bites by the carpet viper and the puff adder. In the laboratory, haematological and other features are noted and immunodiagnosis has a role in species identification. Immobilisation of the bitten limb is probably the single most important first aid measure. Antivenom should be used cautiously when indicated. As only 8.5 percent of snake bite victims attend hospitals in Nigeria, health education should be the main preventive measure, mean-while, the study of immunisation of occupationally predisposed individuals in endemic areas should be intensified. A new Fab fragment antivenom specific to Nigerian Echis ocellatus was investigated clinically, just as the local herbs-Aristolochia spp, Guiera spp and Schummaniophyton spp are investigated experimentally.

Recombinant expression of a selective blocker of M(1) muscarinic receptors.

Mamba venoms contain peptides with high selectivity for muscarinic receptors. Due to the limited availability of the M(1) muscarinic receptor-selective MT7 or m1-toxin 1, the peptide was expressed in Sf9 cells using a synthetic cDNA and purified. The isolated peptide had over four orders of magnitude higher affinity for the M(1) compared to M(2)-M(5) muscarinic receptors. The peptide strongly inhibited Ca(2+) mobilisation through recombinant and endogenously expressed M(1) receptors, having no effect on the function of the other subtypes. The MT7 peptide provides a unique tool for identification and functional characterisation of M(1) receptors in cells and tissues.