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A T Tu

Publications and source records attributed to A T Tu.

At least 19 recordsLinked to original sources
PubMed2001

Purification, sequencing, and phylogenetic analyses of novel Lys-49 phospholipases A(2) from the venoms of rattlesnakes and other pit vipers.

Basic phospholipase A(2) homologs with Lys49 substitution at the essential Ca(2+)-binding site are present in the venom of pit vipers under many genera. However, they have not been found in rattlesnake venoms before. We have now screened for this protein in the venom of rattlesnakes and other less studied pit vipers. By gel filtration chromatography and RP-HPLC, Lys49-phospholipase-like proteins were purified from the venoms of two rattlers, Crotalus atrox and Crotalus m. molossus, and five nonrattlers, Porthidium nummifer, Porthidium godmani, Bothriechis schlegelii, Trimeresurus puniceus, and Trimeresurus albolabris. Their N-terminal amino acid sequences were shown to be characteristic for this phospholipase subfamily. The purified basic proteins from rattlesnakes caused myonecrosis and edema in experimental animals. We have also cloned the cDNAs and solved the complete sequences of four novel Lys49-phospholipases from the venom glands of C. atrox, P. godmani, B. schlegelii, and Deinagkistrodon acutus (hundred-pace). Phylogenetic analyses based on the amino acid sequences of 28 Lys49-phospholipases separate the pitviper of the New World from those of the Old World, and the arboreal Asiatic species from the terrestrial Asiatic species. The implications of the phylogeny tree to the systematics of pit vipers, and structure-function relationship of the Lys49-phospholipases are discussed.

Amino Acid Substitution↗
PubMed2001

Characterization of hyaluronidase isolated from Agkistrodon contortrix contortrix (Southern Copperhead) venom.

Snake venoms are a rich source of enzymes including many hydrolytic enzymes. Some enzymes such as phospholipase A2, proteolytic enzymes, and phosphodiesterases are well characterized. However many enzymes, such as the glycosidase, hyaluronidase, have not been studied extensively. Here we describe the characterization of snake venom hyaluronidase. In order to determine which venom was the best source for isolation of the enzyme, the hyaluronidase activity of 19 venoms from Elapidae, Viperidae, and Crotalidae snakes was determined. Since Agkistrodon contortrix contortrix venom showed the highest activity, this venom was used for purification of hyaluronidase. Molecular weight was determined by matrix-assisted laser desorption ionization mass spectroscopy and was found to be 59,290 Da. The molecular weight value as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was 61,000 Da. Substrate specificity studies indicated that the snake venom enzyme was specific only for hyaluronan and did not hydrolyze similar polysaccharides of chondroitin, chondroitin sulfate A (chondroitin 4-sulfate), chondroitin sulfate B (dermatan sulfate), chondroitin sulfate C (chondroitin 6-sulfate), chondroitin sulfate D, chondroitin sulfate E, or heparin. The enzyme is an endo-glycosidase without exo-glycosidase activity, as it did not hydrolyze p-nitrophenyl-beta-D-glucuronide or p-nitrophenyl-N-acetyl-beta-D-glucosaminide. The main hydrolysis products from hyaluronan were hexa- and tetrasaccharides with N-acetylglucosamine at the reducing terminal. The cleavage point is at the beta1,4-glycosidic linkage and not at the beta1,3-glycosidic linkage. Thus, snake venom hyaluronidase is an endo-beta-N-acetylhexosaminidase specific for hyaluronan.

Agkistrodon↗
PubMed2001

Analyses of snake venom for forensic investigation.

Snake venoms are responsible for two reported human deaths as determined by the double diffusion method. Double diffusion is a simple, rapid, and reliable method, but it is rather qualitative and requires a rather large quantity of sample. In order to evaluate venom concentration more quantitatively, the more sensitive ELISA (enzyme linked immunosorbent assay) method was used as an alternative, and the results were compared with that of the double diffusion method.

Adult↗
PubMed2000

A snake venom inhibitor to muscarinic acetylcholine receptor (mAChR): isolation and interaction with cloned human mAChR.

An inhibitor to the muscarinic acetylcholine receptor (mAChR) was purified from the venom of Crotalus atrox (western diamondback rattlesnake). The inhibitor was found to be a 30-kDa homodimer protein with phospholipase A2 activity. In order to determine the subtype selectivity of the purified inhibitor, the inhibitory effect on the binding of two orthosteric antagonists, [3H]quinuclidinyl benzilate ([3H]QNB) and [3H]N-methylscopolamine methyl chloride ([3H]NMS), to five subtypes of cloned human mAChR was tested. The purified inhibitor reduced the binding of [3H]QNB and/or [3H]NMS to all subtypes of the mAChR while showing the highest inhibitory effect on the M5 subtype. The Kd values of the receptors for the antagonists were increased in the presence of the inhibitor; however, the Bmax values were not changed. The effects of the purified inhibitor on the dissociation of [3H]NMS from the receptors were also investigated. Dissociation of the antagonist was remarkably slowed down by addition of the inhibitor. These findings may suggest an allosteric action of the purified inhibitor. In addition, the present study indicates that the presence of mAChR inhibitors is quite common in snake venoms.

Animals↗
PubMed1999

Muscarinic acetylcholine receptor (mAChR) inhibitor from snake venom: interaction with subtypes of human mAChR.

Snake venoms can contain a variety of well-studied neurotoxins, especially nicotinic acetylcholine receptor inhibitor, normally called postsynaptic neurotoxin. Karlsson first reported muscarinic acetylcholine receptor (mAChR) inhibitor from snake venom. In a previous study in our laboratory, we found a mAChR inhibitor from Naja naja sputatrix venom that bound to rat brain synaptosomes. Brain synaptosomes contain all subtypes of mAChRs, and thus the exact selectivity of the inhibitor could not be determined. mAChR inhibitor from N. naja sputatrix venom was purified and the binding to all human mAChR subtypes (M1, M2, M3, M4, and M5) was investigated and is reported in this communication. The inhibitor bound to all subtypes of the human mAChR, but showed considerably high selectivity for the M5 subtype. It was also found that the reduction of disulfide bonds in the inhibitor eliminated the binding to the mAChR. This suggests that a specific tertiary conformation maintained by disulfide bonds is essential for binding to the mAChR. An oligo peptide, QIHDNCYNE, comparable to a part of the inhibitor molecule, was synthesized and studied for its binding to the mAChR. The synthetic peptide did not show any binding activity, suggesting this portion of the inhibitor molecule is not involved in mAChR binding. The selective binding of the M5 mAChR subtype to antagonists has not yet been reported. Therefore, the purified inhibitor reported in this communication may be a useful tool to clarify the mechanism of muscarinic cholinergic transmission.

Amino Acid Sequence↗
PubMed1998

Biochemical characterization of lebetase, a direct-acting fibrinolytic enzyme from Vipera lebetina snake venom.

Lebetase, the fibrinolytic enzyme isolated from Vipera lebetina (Levantine viper) snake venom is a metalloenzyme that contains one mole of Zn2+ and one mole of Ca2+ per mole of protein. Lebetase is inhibited by dithiothreitol, suggesting that disulfide bonds are necessary for holding the structure. Vipera lebetina venom contains several isoforms of lebetase in the interval of pI 4.6-5.4. Two lebetase fractions I (pI of the main component 5.0) and II (pI of the main component 5.3) degrade fibrin and fibrinogen by hydrolysis of the alpha and beta chains. The molecular weights of the cleavage products produced by the two different lebetase fractions are identical. The metal ions, Cd2+, Cu2+, Co2+, inhibit fibrinolytic and caseinolytic activity of lebetase I and II. Using mass spectrometry we characterized differences in molecular masses of lebetase I and II (22719 Da and 22912 Da). Vipera lebetina venom from a single snake contains mainly one form of lebetase. Lebetase I is more stable at low pH than lebetase II. The lebetases I and II inhibit platelet aggregation induced by ADP in a dose-dependent manner.

Adenosine Diphosphate↗
PubMed1997

The nucleotide sequence of the translated and untranslated regions of a cDNA for myotoxin a from the venom of prairie rattlesnake (Crotalus viridis viridis).

Myotoxin a, isolated from C. viridis viridis venom, is a myonecrotizing agent present in many snake venoms. A cDNA library was prepared from mRNA obtained from the venom glands of a C. viridis viridis. The complete base sequence of a cDNA corresponding to an mRNA encoding myotoxin a was determined. The 5' untranslated region has 15 nucleotides, while the 3' untranslated region has 109 nucleotides. The translated portion of the myotoxin a cDNA encodes a start methionine, a signal peptide, the myotoxin a peptide sequence, and an additional lysine residue. It is likely that myotoxin a is secreted as the cDNA encodes a signal peptide immediately 5' to the myotoxin a peptide code.

Amino Acid Sequence↗
PubMed1997

Structure and other chemical characterizations of gila toxin, a lethal toxin from lizard venom.

The complete primary structure of a lethal toxin, horridum toxin, from the venom of the lizard, Heloderma horridum horridum, was determined by Edman degradation. The amino acid sequence was deduced by overlapping peptide fragments generated by chemical and enzymatic digestions. Horridum toxin causes hemorrhage in internal organs and particularly in the eye, leading to exophthalmia, an effect that has not been observed for other toxins. It is a glycoprotein with a total of 210 residues. Examination of the primary sequence revealed that horridum toxin has considerable homology to tissue-type kallikrein and trypsin. Furthermore, synthetic substrates for trypsin, such as tosyl-L-arginine methyl ester, benzoyl-L-arginine ethyl ester and other p-nitroanilide substrates, were hydrolyzed. The toxin released bradykinin upon hydrolysis of kininogen. This enzymatic behavior is similar to that of plasma kallikrein: however, the presence of a characteristic "kallikrein-like" loop at 91-100 (GTIYNCNYVN) in the primary structure and other features similar to tissue kallikrein suggest that horridum toxin is more like tissue kallikrein. This toxin degraded all three chains of fibrinogen but did not form a clot, which suggests that it is different from thrombin. Moreover, it differs from another lethal factor from H. horridum horridum, gila toxin, which has 245 amino acid residues and does not cause exophthalmia.

Amino Acid Sequence↗
PubMed1996

cDNA cloning and deduced amino acid sequence of fibrinolytic enzyme (lebetase) from Vipera lebetina snake venom.

The complete amino acid sequence of lebetase is deduced from the nucleotide sequence of a cDNA clone isolated by screening a venomous gland c DNA library of Central Asian Vipera lebetina snake. The cDNA sequence with 2011 basepairs encodes an open reading frame of 478 amino acids which includes an 18 amino acid signal peptide, plus an 175 amino acid segment of zymogen-like propeptide, a mature protein of 204 amino acids, a spacer of 18 amino acids and a disintegrin-like peptide of 63 amino acids. The mature protein lebetase as isolated from the crude venom has the molecular weight of approximately 23.7 kD and, thus, lebetase as well as several other snake venom metalloproteinases is translated as a precursor protein, which may be processed posttranslationally. The lebetase proprotein has a "cysteine switch" motif (PKMCGV) similar to that involved in the activation of matrix metalloproteinase zymogens. The mature protein (residues 223-427) shows the strongest similarity with fibrolase (63% identity), fibrinolytic enzyme from Agkistrodon contortrix contortrix venom. The metalloproteinase domain has a typical zinc-chelating sequence (HEXXHXXGXXH). In the disintegrin-like domain of protein, the RGD sequence is replaced by VGD.

Amino Acid Sequence↗
PubMed1996

Phospholipase A2 from Naja naja sputatrix venom is a muscarinic acetylcholine receptor inhibitor.

A variety of snake venoms was tested for the ability to inhibit the binding of antagonists to specific muscarinic acetylcholine receptors (mAChRs); the highest activity was found in the venom of Naja naja sputatrix. The active principle in this venom was isolated by column chromatography on Sephadex G-50, Sephadex G-150, and CM-Sephadex C-25. The final preparation was homogeneous as determined by polyacrylamide gel electrophoresis and HPLC; about sevenfold purification was achieved with a yield of 12%. The isolated active component, which was designated "muscarinic inhibitor," was found to displace various antagonists from rat synaptosomal membranes, which contain all subtypes of mAChRs. The m1 and m2 recombinant human receptors were also competitive with N. naja sputatrix muscarinic inhibitor. This antagonist-displacing action was dose dependent, but was independent of the reaction temperature. The isolated muscarinic inhibitor was determined to be a 13.6 kDa, monomeric, neutral protein and to have an N-terminal amino acid sequence which is highly homologous with phospholipase A2 from the venoms of genus Naja. N. naja sputatrix muscarinic inhibitor could hydrolyze phosphatidylcholine in a dose- and temperature-dependent manner. This phospholipase A2 enzymatic activity was augmented by the addition of the calcium ion, while it was almost completely abolished by a competitive inhibitor of phospholipase A2 enzymes. However, the antagonist-displacing activity was only slightly affected by these agents. The treatment of the muscarinic inhibitor with p-bromophenacyl bromide, which selectively modifies the histidine residue in the catalytic site of a phospholipase A2 enzyme, caused completed elimination of both activities. These findings indicate that N. naja sputatrix muscarinic inhibitor is a protein with two distinct activities, phospholipase and antagonist displacement, the active centers of which may be in close physical proximity for both actions. This is the first finding that a phospholipase A2 is an inhibitor of the muscarinic receptor.

Amino Acid Sequence↗
PubMed1996

Cross-reactivities of polyclonal antibodies against lebetase, fibrinolytic enzyme of Levantine viper (Vipera lebetina) venom.

Antibodies to two fractions of fibrinolytic enzyme in Vipera lebetina venom were produced by immunizing mice with chromatographically purified lebetase probes. The antibodies were isolated from mice blood by protein A affinity chromatography. The antibodies to both fractions reacted only with the fibrinolytic enzyme in V. lebetina venom as demonstrated by western immunoblotting. Immunodot assays, ELISA and western immunoblotting revealed that 11 snake venoms including species of Viperidae and Crotalidae but not Elapidae cross-react with lebetase antibodies to varying degrees. The molecular weights of cross-reacting components were detected and compared with the earlier published data.

Animals↗
PubMed1995

Nucleotide sequence encoding the snake venom fibrinolytic enzyme atroxase obtained from a Crotalus atrox venom gland cDNA library.

Atroxase, isolated from the venom of Crotalus atrox (western diamondback rattlesnake), is a nonhemorrhagic protease which has fibrinolytic activity in vivo. The primary structure of atroxase was deduced from the cDNA encoding the atroxase protein. The venom glands of Crotalus atrox were used to prepare a cDNA library. Degenerate oligonucleotides were synthesized based on the partial amino acid sequence of atroxase and were used as primers in the polymerase chain reaction to amplify overlapping cDNA fragments from the C. atrox cDNA library. The resulting cDNA fragments were subcloned, sequenced, and translated. The final nucleotide sequence shows high homology to previously described primary structures of nonhemorrhagic fibrinolytic proteases isolated from snake venom.

Amino Acid Sequence↗
PubMed1995

Biochemical characterization of basilase, a fibrinolytic enzyme from Crotalus basiliscus basiliscus.

Snake venoms, especially from the Crotalidae family, contain a variety of enzymes that prevent blood coagulation by virtue of their fibrinolytic enzymes. Nineteen snake venoms were screened for fibrinolytic activity and the highest activity was found in the venom of Crotalus basiliscus basiliscus venom. The active principle, basilase, was isolated, purified, and found to have fibrinolytic and fibrinogenolytic activity. It had a molecular weight of 22,000 and 1 mol of zinc per mole of protein associated with it. The proteolytic activity of the enzyme against dimethyl casein was inhibited by ethylenediaminetetraacetic acid and alpha 2-macroglobulin. It did not inactivate alpha 2-macroglobulin. Basilase did not have any of the following activities: thrombin-like, factor X-like, protein C activating, or urokinase-like. It caused neither hemorrhage nor platelet aggregation. In spite of its proteolytic activity, basilase did not hydrolyze the membranes of platelets. Basilase had 24% alpha-helix, 31% beta-sheet, 25% turns, and 20% unordered structure, as determined by Fourier Transform Infrared spectroscopy. Basilase is an enzyme that hydrolyzes fibrin directly without activation of plasminogen.

Amino Acid Sequence↗
PubMed1994

Calsequestrin is a major binding protein of myotoxin alpha and an endogenous Ca2+ releaser in sarcoplasmic reticulum.

Myotoxin alpha from prairie rattlesnakes induced Ca2+ release from the heavy fraction of sarcoplasmic reticulum at submicromolar concentrations. 125I-Labeled myotoxin alpha (125I-myotoxin alpha) specifically bound to the heavy fraction. Fractionation of the solubilized heavy fraction with a spermine-agarose column gave purified calsequestrin as a major binding protein of 125I-myotoxin alpha. We have first indicated that calsequestrin is a target protein for Ca(2+)-releasing action of myotoxin alpha. Calsequestrin probably plays a key role in physiological Ca2+ release from sarcoplasmic reticulum.

Animals↗
PubMed1994

FT-IR and near-infrared FT-Raman studies of the secondary structure of insulinotropin in the solid state: alpha-helix to beta-sheet conversion induced by phenol and/or by high shear force.

Insulinotropin (glucagon-like peptide I) is a peptide containing 31 amino acid residues. It stimulates the secretion of the hormone insulin. The solubility of this peptide is highly dependent on its environment and the treatment that it has undergone. For instance, synthetic insulinotropin is highly soluble in neutral phosphate-buffered saline (1 mg/mL). However, the application of shear force by stirring renders it extremely insoluble (1 micrograms/mL). This property may be explained in terms of a change in peptide secondary structure with no alteration in primary structure. In order to understand this phenomenon, FT-IR and near-IR FT-Raman were employed to examine four samples prepared under different experimental conditions. It was found that solubility decreases as the alpha-helix is converted to an antiparallel beta-sheet structure.

Amino Acid Sequence↗