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J D Shannon

Publications and source records attributed to J D Shannon.

10 recordsLinked to original sources
PubMed1992

Sequence of a cDNA clone encoding the zinc metalloproteinase hemorrhagic toxin e from Crotalus atrox: evidence for signal, zymogen, and disintegrin-like structures.

The sequence of two overlapping cDNA clones for the zinc metalloproteinase hemorrhagic toxin e (also known as atrolysin e, EC 3.4.24.44) from the venom gland of Crotalus atrox, the Western diamondback rattlesnake, is presented. The assembled cDNA sequence is 1975 nucleotides in length and encodes an open reading frame of 478 amino acids. The mature hemorrhagic toxin e protein as isolated from the crude venom has a molecular weight of approximately 24,000 and thus represents the processed product of this open reading frame. From the deduced amino acid sequence, it can be hypothesized that the enzyme is translated with a signal sequence of 18 amino acids, an amino-terminal propeptide of 169 amino acids, a central hemorrhagic proteinase domain of 202 amino acids, and a carboxy-terminal sequence of 89 amino acids. The propeptide has a short region similar to the region involved in the activation of matrix metalloproteinase zymogens. The proteinase domain is similar to other snake venom metalloproteinases, with over 57% identity to the low molecular weight proteinases HR2a and H2-proteinase from the Habu snake Trimeresurus flavoviridis. The carboxy-terminal region, which is not observed in the mature protein, strongly resembles the protein sequence immediately following the proteinase domain of HR1B (a high molecular weight hemorrhagic proteinase from the venom of T. flavoviridis) and the members of a different family of snake venom polypeptides known for their platelet aggregation inhibitory activity, the disintegrins. The cDNA sequence bears striking similarity to a previously reported sequence for a disintegrin cDNA. This report is evidence that this subfamily of venom metalloproteinases is synthesized in a proenzyme form which must be proteolytically activated.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Proteolytic digestion of non-collagenous basement membrane proteins by the hemorrhagic metalloproteinase Ht-e from Crotalus atrox venom.

Hemorrhagic toxin e (Ht-e), a metalloproteinase isolated from the venom of the Western Diamondback rattlesnake Crotalus atrox, digests laminin and nidogen, both in their isolated forms and when present in a purified soluble complex. The only common site of cleavage by Ht-e of isolated nidogen and nidogen when complexed with laminin is at amino acid residue 336 in the amino terminal domain. Additionally, nidogen in complex with laminin is also cleaved at sites 322, 351 and 840 as determined by sequence analysis and site 953 as proposed from the molecular mass of a digestion product. Isolated nidogen, on the other hand, was cleaved at amino acid residues 75, 336, 402, and 920, as determined by sequence determinations and approximately at residues 296, 478, 625 and 702 as proposed from the molecular mass values of the generated polypeptide chains. Products from the proteolytic cleavage of the A and B2 chains of laminin were observed with the sites of cleavage determined to be at position 2666 in the laminin A chain and position 1238 in the laminin B2 chain. The laminin digestion products were identical regardless of whether nidogen was present in a complex with the laminin chains.

Amino Acid Sequence↗
PubMed1991

Synthetic and endogenous inhibitors of snake venom metalloproteinases.

The venoms of most Crotalidae snakes contain metalloproteinases which are the agents responsible for the production of venom-induced hemorrhage via proteolytic destruction of capillary basement membranes. Prevention of hemorrhage by administration of antiserum is generally not totally effective against damage at the site of envenomation. Therefore, we have investigated alternate methods for the alleviation of hemorrhage by inhibition of the proteolytic activity of the hemorrhagic toxins. The first approach involves the synthesis of carboxyalkyl peptide inhibitors in which the peptide moiety is modeled on the substrate specificity of the toxins. With this approach we have determined that the carboxypentyl group for interaction with the active site Zn+ +ion is most effective. Also, longer peptide moieties enhance the inhibitors' activity giving Ki's in a range of 10(-6) M. Our second approach to hemorrhagic toxin inhibition was to search for the presence of endogenous inhibitors against the toxins in the venom. From the crude venom we have isolated several pyro-glutamate containing peptides, two of which are relatively good inhibitors of the toxins. The isolation and characterization of the endogenous toxin inhibitors as well as the synthetic inhibitors may ultimately serve as a basis for new, effective treatments against venom-induced hemorrhage.

Amino Acid Sequence↗
PubMed1990

Interaction of hemorrhagic metalloproteinases with human alpha 2-macroglobulin.

The interaction between four Crotalus atrox hemorrhagic metalloproteinases and human alpha 2-macroglobulin was investigated. The proteolytic activity of the hemorrhagic toxins Ht-c, -d, and -e against the large molecular weight protein substrates, gelatin type I and collagen type IV, was completely inhibited by alpha 2-macroglobulin. The proteolytic activity of Ht-a against the same substrates was not significantly inhibited. Each mole of alpha 2-macroglobulin bound maximally 2 mol of Ht-e and 1.1 mol of Ht-c and Ht-d. These proteinases interacted with alpha 2-macroglobulin rapidly at 22 degrees C. Rate constants based on intrinsic fluorescence measurements were 0.62 X 10(5) M-1 s-1 for interaction of alpha 2-macroglobulin with Ht-c and -d and 2.3 X 10(5) M-1 s-1 for the interaction of alpha 2-macroglobulin with Ht-e. Ht-a interacted with alpha 2-macroglobulin very slowly at 22 degrees C. Increasing the temperature to 37 degrees C and prolonging the time of interaction with alpha 2-macroglobulin resulted in the formation of Mr 90,000 fragments and high molecular weight complexes (Mr greater than 180,000), in which Ht-a is covalently bound to the carboxy-terminal fragment of alpha 2-M. The identification of the sites of specific proteolysis of alpha 2-macroglobulin shows that the cleavage sites for the four metalloproteinases are within the bait region of alpha 2-macroglobulin. Ht-c and -d cleave only at one site, the Arg696-Leu697 peptide bond, which is also the site of cleavage for plasmin, thrombin, trypsin, and thermolysin. Ht-a cleaves alpha 2-macroglobulin primarily at the same site, but a secondary cleavage site at the His694-Ala695 peptide bond was also identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

Identification of the cleavage sites by a hemorrhagic metalloproteinase in type IV collagen.

Type IV collagen, solubilized from Engelbreth-Holm-Swarm (EHS) tumor basement membranes is digested by a hemorrhagic metalloproteinase, Ht-e, isolated from the crude venom of the Western Diamondback rattlesnake, Crotalus atrox. The major proteolytic products have Mr 141,000, 132,000, 87,000, 71,000, 33,000 and approximately 18,000 as estimated by SDS-gel electrophoresis of pepsinized type IV collagen fragments. Sequence analysis of the digestion products reveal that the Mr 141,000, 71,000 and approximately 18,000 band are derived from the alpha 1(IV) chains and the Mr 132,000, 87,000 and 33,000 bands are derived from the alpha 2(IV) chain. The products are stable over 72-hour incubation periods. The cleavage sites on the alpha 1(IV) and alpha 2(IV) chains are not identical. The alpha 1(IV) chains are cleaved in a pepsin susceptible triplet interruption region of the triple helix at position Ala258-Gln259. The alpha 2(IV) chain is cleaved in the triple helical region near the NC2 domain at the Gly191-Leu192 peptide bond. Isolated hexameric NC1 globular domains of type IV collagen are not digested by Ht-e. The present study demonstrates that the venom hemorrhagic metalloproteinase Ht-e has type IV collagenolytic activity. The triple helix of the type IV collagen molecule is cleaved in a region located immediately carboxyl to the flexible NC2 domain. The degradation by Ht-e of type IV collagen, a major component of basement membranes which forms the scaffold of this extracellular structure, may account in part for the hemorrhagic activity of this toxin.

Amino Acid Sequence↗
PubMed1990

Small-group interactive computer-assisted teaching.

A form of teaching developed at the Montreal General Hospital over the past 6 years which involves small groups of students, a tutor and computer assistance is described. The major supposition of the paper is that constant interaction with students on a question-and-answer basis is the most efficient form of teaching. With this method, areas of weakness and lack of comprehension of concepts can be easily and rapidly identified. Patient Management Problems (PMPs) on the computer are used in order to supply the questions that constitute the basis of the tutorial. These questions may then be expanded upon by the personal experience of the tutor. The feedback to the student inherent in this method allows for immediate rectification of problems. An attempt is made to validate the efficacy of this form of teaching with a literature review.

Clinical Competence↗
PubMed1989

Degradation of extracellular matrix proteins by hemorrhagic metalloproteinases.

The proteolytic activity of four hemorrhagic metalloproteinases (Ht-a, c, d, and e) isolated from the venom of the Western diamondback rattlesnake (Crotalus atrox) was investigated using isolated extracellular matrix (ECM) proteins. We determined that all of the proteinases are capable of cleaving fibronectin, laminin, type IV collagen, nidogen (entactin), and gelatins. However, none of the proteinases were proteolytic against the interstitial collagen types I and III or type V collagen. With all of the substrates listed above Ht-c and Ht-d produced identical digestion patterns, as would be expected for these isoenzymes. With fibronectin, Ht-a produces a different ratio of products from Ht-c and Ht-d, while Ht-e produces a unique pattern of digestion. Ht-e and Ht-a produced nonidentical patterns with the laminin/nidogen preparation although some similarity was shared between them as well as with the Ht-c/d digestion pattern. Similar results were also observed for these proteinases with nidogen 150 as the substrate. The type IV collagen digestion patterns by Ht-e and Ht-a were similar to the pattern observed with Ht-c/d but differed by two bands. The digestion patterns of the three gelatins produced by the proteinases show differences between Ht-c and Ht-d when compared to Ht-e and Ht-a. This investigation clearly shows that several of the ECM proteins are efficiently digested by these toxins. The proteinases have some digestion sites in common but show differing specificities. In addition, the range of ECM proteins digested by these hemorrhagic proteinases is nearly identical to that demonstrated by the ECM proteinase stromelysin (MMP-3). From these data, and the knowledge of the roles these ECM proteins have in maintaining basement membrane structural/functional integrity, one can envision that the degradation of these ECM proteins could readily lead to loss of capillary integrity resulting in hemorrhage occurring at those sites.

Animals↗
PubMed1989

Amino acid sequence of a Crotalus atrox venom metalloproteinase which cleaves type IV collagen and gelatin.

The hemorrhagic toxin Ht-d from venom of the Western diamondback rattlesnake is a metalloproteinase with a molecular weight of 23,234. Peptides were obtained from enzymatic and chemical digestions, separated by reverse-phase chromatography, and sequenced in a gas-phase sequenator. The sequence showed a putative zinc binding site similar to that of thermolysin and other metalloproteinases but no overall significant similarity to the sequences of other metalloproteinases and may represent a new subfamily of metalloproteinases. Ht-d was shown to degrade type IV collagen and gelatin types I, III, and V but not interstitial collagens. The digestion of type IV collagen and other basement membrane proteins may allow this proteinase to disrupt capillary membranes causing hemorrhage in surrounding tissues.

Amino Acid Sequence↗
PubMed1979

Isolation and characterisation of peptide hydrolases from the maize root.

The maize root has two main proteinase and carboxypeptidase components. Proteinase I and carboxypeptidase I, which predominate in older plants, appear to have a serine group at their active sites and have been estimated to have molecular weights of approximately 54000 and 77000 respectively. Proteinase I, which has been purified up to 500-fold, degrades haemoglobin and azocasein with maximum activity at pH 4 and 9--10 respectively, while on maize root protein it gives most hydrolysis in the neutral pH range. The main portion of the nitrate-reductase-inactivating activity in the maize root extract is due to proteinase I. Carboxypeptidase I, like several other plant carboxypeptidases such as carboxypeptidase C which have now (IUB Recommendations 1978) been classified as serine carboxypeptidases (EC 3.4.16.1), has maximum activity around pH 5 and has esterase activity. A second group of proteases, proteinase II and carboxypeptidase II, separated from the above on carboxymethyl-cellulose, were shown to have different molecular weight properties and be equally sensitive to serine and thiol group inhibitors. Proteinase II degrades haemoglobin, but not azocasein and does not mediate nitrate reductase inactivation. Associated with this second group of proteases was a macromolecular component which inactivated nitrate reductase but, unlike the action of proteinase I, was not inhibited by phenylmethylsulphonyl fluoride or casein. It was inhibited by metal chelating agents which were without effect on nitrate reductase inactivation due to proteinase I.

Aging↗