Journal of natural toxins最新文献

Three bioactivity-variant neurotoxins, BmK M1, M4, and M8, have been purified from venom of the Chinese scorpion Buthus martensii Karsch. They possess distinct toxic activity on mice in vivo with different electrostatic properties. The relative toxicities of BmK M1, M4, and M8 are 13.3:2.5:1, which interestingly correspond to their respective pI values, ranging from basic to acidic, of 9.01, 7.53, and 5.30, respectively. In addition, the X-ray crystal structure of BmK M8, which is acidic and 1100 times less active than the most potent and basic alpha-toxin AaH II, have been determined at 1.85 A resolution and analyzed in detail. In combination with information from chemical modifications and site-directed mutagenesis, the structural comparisons and sequence alignments suggest a multisite binding mode for toxin-receptor interactions, and three "toxic regions" with relevance to the binding process, including Face A, Face B, and Site C. Face A is featured in the presence of several aromatic residues and may be more essential for the binding; Face B may contribute to the high efficacy of the binding process, on which substitution by acidic residues could weaken the toxic activity; Site C is probably involved in binding site specificity. The main residues involved in these regions will be discussed.

Phospholipases A2 were purified from the venoms of Asian monotypic crotalinae snakes including Callosellasma, Hypnale, Deinagkistrodon, and Tropidolaemus by a combination of gel filtration and reversed-phase chromatographic methods. One to four isoforms of the enzyme were found in each of the venoms. The venom enzymes were subjected to N-terminal sequencing up to the 30th amino acids, and their molecular weights were analyzed by electrospray-ionization mass spectrometry. Homologous antiplatelet phospholipase with a conserved Glu 6 residue was found in each of the venoms. Basic phospholipases with Trp 6 (W6) but without detectable enzyme activities were also isolated from the venom of C. rhodostoma, H. hypnale, and T. wagleri. These W6 enzymes showed strong heparin-binding affinity and capable of inducing edema in rat paws. The fact that the venoms of Callosellasma and Hypnale contain similar types of phospholipases is in accord with recent reports that these two taxa formed a clade. Deinagkistrodon venom does not contain phospholipase variants other than the Glu-6 subtype as Trimeresurus, Agkistrodon, and Protobothrops venoms do. Interestingly, the Glu-6 enzyme from T. wagleri venom has a molecular weight of 15,319 Daltons, higher than those of most other venom phospholipases. Our results show that new types of the enzyme are more likely to be found in the venom of monotypic species; the amino acid sequence data or the subtypes of venom-phospholipases are potentially useful as markers or a character system for studying higher-order systematics of venomous snakes.

The biological activity and toxicity of crude venom from Conus betulinus, which was collected from the South China Sea, were studied. The venom shows Ach receptor activity, K+ current effect, and low toxicity. Four peptide components, named BeTXIa, BeTXIb, BeTXIIa, and BeTXIIb, were purified by gel-filtration with Sephadex followed by HPLC, and finally sequenced on an ABI model 491 sequencer. The low-molecular-weight peptides BeTXIa and b have 14 and 15 amino acid residues, respectively, while BeTXIIa and b have 27 and 30 amino acid residues, respectively. The results indicate that BeTXs from the venom of C. betulinus are a set of small peptides with a high cysteine content like known conotoxins. However, it is meaningful to find that these sequences have specific chemical characteristics in their cysteine framework which differ greatly from known cysteine frameworks in conotoxin structures.

The nerve growth factor, NGF, from Chinese cobra Naja naja atra venom was isolated by gel-filtration and ion-exchange chromatography. Cobra NGF was characterized by analytical HPLC techniques as well as SDS-PAGE, and was proven to be a glycoprotein with a mol. wt. of 23 (+/- 2) kD and a pI of 9.2. The amino acid analysis and N-terminal sequencing were performed using conventional methods. Bioassays with cultured chick embryos ganglia and rat pheochromocytoma PC-12 cells revealed a promotion of fiber outgrowth, which is typical of NGF activity. Absence of enzymatic, toxicological, and teratogenic activities were shown by quality inspection. Since 1994, many clinical cases about volunteers receiving NGF treatment have been reported in mainland China. Bioactivities of NGF deal with a wide range of disciplines and technologies. In this paper we will discuss neuronal and non-neuronal effects of NGF treatment. Does the NGF cross the blood-brain barrier by transcytosis into the brain tissue? How is NGF important in wound healing, especially in peripheral nerve injury and diabetic neuritis? NGF may also be useful for male volunteers suffering from sterility, because it is possible that the sexual cells of testis can be promoted to maturity.

Three homology models of trypsin and chymotrypsin inhibitor polypeptides from snake venom of Naja naja naja and Leaf-nosed viper in the unbound state and in complex with trypsin and chymotrypsin were built based on homology to bovine pancreatic trypsin inhibitor (BPTI). These venom inhibitors belong to the Kunitz-type inhibitor family, which is characterized by a distinct tertiary fold with three-conserved disulfide bonds. The general folding pattern in these trypsin and chymotrypsin inhibitor homology models is conserved when compared to BPTI. The respective orientations of the inhibitors bound to trypsin/chymotrypsin are similar to that of BPTI bound to bovine trypsin/chymotrypsin. The principal binding loop structure of the inhibitors fills the active site of enzymes in a substrate-like conformation and forms a series of independent main-chain and side-chain interactions with enzymes. In order to provide the possible fingerprints for molecular recognition at the enzyme-inhibitor interface, a detailed theoretical analysis of the interactions between the principal binding loop of these inhibitors and active site of trypsin/chymotrypsin is performed based on available crystal structural, site-directed mutagenetic, kinetic, and sequence analysis studies. Despite the variations present at different positions of the principal binding loop of trypsin and chymotrypsin inhibitor models from Leaf-nosed viper and cobra Naja naja naja, respectively (designated as LnvTI and NCI), there are favorable subsite binding interactions which are expected to exhibit equally potent inhibitory activity as BPTI. On the contrary, significant mutations at several secondary specificity positions in the Naja naja naja trypsin inhibitor (designated as NTI) are likely to affect different inhibitor-enzyme-subsites interactions. This may explain the observed increased inhibitory activity of this polypeptide on a structural basis.

Ribotoxins are a group of ribosome-inactivating proteins (RIPs) isolated mostly from plants. They inactivate ribosomes by a mechanism as RNA N-glycosidase that removes a specific adenine base from the highly conserved "S/R domain" in the largest ribosomal RNA. In this review, we introduce the major results from our laboratory in recent years on the study of the structure and function of RIPs and ribosomes: [1] Purification and characterization of the enzymatic mechanism of RIPs. Several new RIPs were purified and their RNA N-glycosidase and supercoil-dependent DNA endonuclease activities were studied. [2] The topographical structure of ribosomes. The relationship between the structure and function of ribosomes, especially of the "S/R domain" in rat 28S rRNA, were investigated by means of RIPs and other chemical probes. [3] The cytotoxicity of two RIPs to carcinoma cells. [4] Several new methods for studying RIPs and probing the structure of ribosomes were developed, i.e., radioassays for RNA N-glycosidase, glycoprotein detection by fluorescent labeling on SDS-polyacrylamide gels, and methods for small RNA sequencing.

Pedicellarial lectins (SUL-I, SUL-II, and TGL-I) were purified from the toxopneustid sea urchins, Toxopneustes pileolus and Tripneustes gratilla using gel filtration chromatography, affinity chromatography, and reverse-phase HPLC. SUL-I (Nakagawa et al., 1996) and SUL-II from the large globiferous pedicellariae of T. pileolus are D-galactose-binding lectins with molecular masses of 32 kDa and 23 kDa, respectively; while TGL-I from the globiferous pedicellariae of T. gratilla is a Ca(2+)-independent heparin-binding lectin with a molecular mass of 23 kDa. SUL-I induced mitogenic stimulation on murine splenocytes but TGL-I did not. At higher dose ranges SUL-I exhibited inhibitory effects on the cells. The dual response to SUL-I was effectively inhibited by D-galactose. SUL-I enhanced norepinephrine-induced contraction of isolated rat mesenteric artery with endothelium. When endothelium was removed from the artery, acetylcholine did not relax the norepinephrine-induced contraction. In the same artery the enhancing effect of the contraction by SUL-I was abolished, suggesting that SUL-I acts on the endothelium of mesenteric artery, and may release prostanoids. The present results suggest an extracellular function for SUL-I that may have wide-ranging effects in physiological processes. The primary role of pedicellarial lectins from T. pileolus and T. gratilla might be defense against a foreign body.

Anisodamine is a natural alkaloid drug isolated from the plant Anisodus tanguticus growing in western China. The chemical structure and pharmacological action are just like the cholinergic receptor blocking agents atropine or scopolamine. The specific characteristic of the drug is being able to relieve the dangerous situation of microcirculatory failure, especially in case of DIC or renal failure. The prognosis of the patients will be quite good. Another characteristic of the drug is that no serious toxic reaction occurs even in successive doses given intravenously up to 500 mg a day. This is about fifty times greater than a common dose of 10 mg. Since we begin with the drug as a routine medication for the symptomatic treatment of renal failure, DIC bleeding, and microcirculatory failure, we should say that the specific antivenin and anisodamine are two treasure drugs for snakebites.

The psoralens are photoactivated plant biosynthetic compounds which are found in several plant families, including common fruits and vegetables. Synthetic forms of the psoralens bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen) are extensively used in skin chemotherapy in combination with long-wave ultraviolet radiation (PUVA). Side effects of PUVA therapy are not, however, desirable, and this therapy has been linked with increased incidence of skin cancer in humans. The psoralens are known to be carcinogenic, mutagenic and teratogenic, and to cause photodermatitis. The main objective of this study was to document the effect of PUVA on the epidermis of rats. Female Wistar rats were administered dietary bergapten and/or xanthotoxin (0-200 mg/kg body) and exposed to UVA radiation (45 min./day) for four weeks. At the end of the four-week period the rats were sacrificed; skin samples were taken from the ears and the top part of the tail and fixed for examination by Scanning Electron Microscopy. The animals subjected to PUVA had significantly smaller scales on the tail epidermis (mean scale size for the control 926 mu vs. 725 to 805 mu for the psoralen treatment groups. The rats that received dietary psoralens also had significantly less hair on the ears compared with the control animals (mean number of hairs per millimeter over the ear edge for the control 54.9 vs. 2.00 to 10.7 for the treatment groups). The two compounds were synergistic in their ability to reduce scale size on the tail epidermis.