Do we know the complete sequence of metalloproteinase and nonenzymatic platelet aggregation inhibitor (disintegrin) precursor proteins?

A limited role for gene duplications in the evolution of platypus venom

Gene duplication followed by adaptive selection is believed to be the primary driver of venom evolution. However, to date, no studies have evaluated the importance of gene duplications for venom evolution using a genomic approach. The availability of a sequenced genome and a venom gland transcriptome for the enigmatic platypus provides a unique opportunity to explore the role that gene duplication plays in venom evolution. Here, we identify gene duplication events and correlate them with expressed transcripts in an in-season venom gland. Gene duplicates (1,508) were identified. These duplicated pairs (421), including genes that have undergone multiple rounds of gene duplications, were expressed in the venom gland. The majority of these genes are involved in metabolism and protein synthesis not toxin functions. Twelve secretory genes including serine proteases, metalloproteinases, and protease inhibitors likely to produce symptoms of envenomation such as vasodilation and pain were detected. Only 16 of 107 platypus genes with high similarity to known toxins evolved through gene duplication. Platypus venom C-type natriuretic peptides and nerve growth factor do not possess lineage-specific gene duplicates. Extensive duplications, believed to increase the potency of toxic content and promote toxin diversification, were not found. This is the first study to take a genome-wide approach in order to examine the impact of gene duplication on venom evolution. Our findings support the idea that adaptive selection acts on gene duplicates to drive the independent evolution and functional diversification of similar venom genes in venomous species. However, gene duplications alone do not explain the "venome" of the platypus. Other mechanisms, such as alternative splicing and mutation, may be important in venom innovation.

Insularinase A, a prothrombin activator from Bothrops insularis venom, is a metalloprotease derived from a gene encoding protease and disintegrin domains

The first low-molecular-mass metalloprotease presenting prothrombin activating activity was purified from Bothrops insularis venom and named insularinase A. It is a single-chain protease with a molecular mass of 22 639 Da. cDNA sequence analysis revealed that the disintegrin domain of the precursor protein is post-translationally processed, producing the mature insularinase A. Analysis of its deduced amino acid sequence showed a high similarity with several fibrin(ogen)olytic metalloproteases and only a moderate similarity with prothrombin activators. However, SDS-PAGE of prothrombin after activation by insularinase A showed fragment patterns similar to those generated by group A prothrombin activators, which convert prothrombin into meizothrombin independently of the prothrombinase complex. In addition, insularinase A activates factor X and hydrolyses fibrinogen and fibrin. Chelating agents fully inhibit all insularinase A activities. Insularinase A induced neither detachment nor apoptosis of human endothelial cells and was also not able to trigger an endothelial proinflammatory cell response. Nitric oxide and prostacyclin levels released by endothelial cells were significantly increased after treatment with insularinase A. Our results show that, although its primary structure is related to class P-I fibrin(ogen)olytic metalloproteases, insularinase A is functionally similar to group A prothrombin activators.

Purification, characterization, and cDNA sequence of halysetin, a disintegrin-like/cysteine-rich protein from the venom of Agkistrodon halys Pallas

By means of DEAE-Sepharose CL-6B column chromatography, gel filtration on Sephadex G-75 and Superose 12 FPLC, halysetin, an antiplatelet protein, was purified from the venom of Agkistrodon halys Pallas with molecular mass of 29 kDa on SDS-PAGE and 23,168 Da by mass spectrometry. The p1 was about 5.0. Halysetin was devoid of phospholipase A2, fibrino-(geno)lytic, esterase, hemorrhagenic activities. Halysetin dose-dependently inhibited the aggregation of human platelet, which was stimulated by collagen with IC50 of 420 nM, but not that stimulated by ADP. The N-and C-terminal sequences of halysetin were characterized. Its full-length cDNA was cloned by RT-PCR from the total RNA extracted from the snake venom gland. It encoded a protein of 212-amino-acid residues with disintegrin-like/cysteine-rich domains and was highly homologous with SYMPs (snake venom metalloprotease).

Identification of bothrojaracin-like proteins in snake venoms from Bothrops species and Lachesis muta

Bothrojaracin, a 27 kDa protein isolated from Bothrops jararaca venom, forms a non-covalent complex with thrombin, thus blocking its activity. We have previously identified a bothrojaracin-like protein in B. alternatus venom [Castro, H.C., Dutra, D.L.S., Oliveira-Carvalho, A.L., Zingali, R.B., 1998. Bothroalternin, an inhibitor of thrombin from the venom of Bothrops alternatus. Toxicon 36, 1903-1912]. In this report, we have examined snake venoms from six different Bothrops species (B. atrox, B. cotiara, B. jararacussu, B. moojeni and B. neuwiedi), from Lachesis muta and from Crotalus durissus terrificus for the presence of bothrojaracin-like proteins, which we define here as 27 kDa proteins that are immunologically related to bothrojaracin and that inhibit thrombin-induced platelet aggregation. The immunological analysis of these venoms by different techniques indicated the existence of at least one protein recognized by anti-bothrojaracin serum in all venoms tested. Bothrojaracin-like proteins were purified from all crude venoms, except for C. d. terrificus, by a single-step procedure using a thrombin affinity column (PPACK-thrombin-Sepharose). Retained material that inhibits thrombin-induced platelet aggregation was found in a different proportion in each species. Under non-reducing conditions, SDS-PAGE of this material revealed several bands between 20-60 kDa; only those bands corresponding to 27 kDa were recognized by anti-bothrojaracin serum. ELISA confirmed the greater bothrojaracin immunoreactivity of proteins present in B. atrox and B. cotiara as compared to other Bothrops species. Smaller amounts of proteins related to bothrojaracin were found in L. muta venom and were absent from the venom of C. d. terrificus. Our results thus suggest that bothrojaracin-like proteins are widely distributed among Bothrops genera.

A novel high molecular weight fibrinogenase from the venom of Bitis arietans

A fibrinogenase (Ba100) with an apparent molecular mass of 100 kDa under non-reducing conditions and a pI of 5.4 was purified from the venom of the African puff adder (Bitis arietans) by fibrinogen affinity chromatography. Under reducing conditions the protease dissociates into subunits of 21 kDa and 16 kDa. N-Terminal amino acid sequencing showed these two chains to have 66.7% homology and homology to C-type lectins. The fibrinogenase activity of Ba100 cleaves the Aalpha and Bbeta chain of fibrinogen rendering the molecule unable to polymerise into fibrin clots. Ba100 inhibited platelet aggregation in platelet rich plasma, and clot formation in whole blood, in a concentration dependent manner.

Snake venom hemorrhagins

Viperine and crotaline snake venoms contain one or more hemorrhagic principles called hemorrhagins. These are zinc-containing metalloproteases characterized by the presence of a protease domain, with additional domains in some of them. They act essentially by degrading the component proteins of basement membrane underlying capillary endothelial cells. The toxins also act on these cells causing lysis or drifting apart, resulting in hemorrhage per rhexis or per diapedesis. Some of these toxins have been found to exert additional effects such as fibrinogenolysis and platelet aggregation that facilitate hemorrhage. The structural and functional features of this class of toxins have been discussed in this review in an attempt to get a better understanding of their toxicity. This can be of immense therapeutic value in the management of snake venom poisoning, as hemorrhagins are among the major lethal factors in snake venom.

Pharmacological activity of the interdomain segment between metalloproteinase and disintegrin domains

Metalloproteinases (haemorrhagic or non-haemorrhagic), disintegrins and most probably C-type lectin-related proteins are derived by the proteolysis of a common precursor protein. There is a short interdomain segment between the metalloproteinase and disintegrin domains which will be released into the venom. To determine whether this region of the molecule contributes to the biological role of the precursors or the products derived by the proteolysis of the precursors, we synthesized a peptide based on this short segment and examined its toxicity and biological activity. The synthetic peptide did not show any lethal toxicity, anticoagulant and antiplatelet effects. However, the peptide appeared to lower the blood pressure or normotensive rats upon infusion, but did not affect the blood levels of triglyceride, total cholesterol, high-density lipoproteins or low-density lipoproteins. The peptide, however, failed to exhibit any effect on spontaneously hypertensive rats and hence may not have a potential as an antihypertensive agent. Based on these results, we conclude that this interdomain segment may not contribute significantly to the biological activity of precursor proteins.

Are C-type lectin-related proteins derived by proteolysis of metalloproteinase/disintegrin precursor proteins?

Metalloproteinases and disintegrins, non-enzymatic inhibitors of platelet aggregation, are derived by proteolysis from common precursors. A closer examination of the cDNA and amino acid sequences of these precursors indicated that the putative signal peptide may be an internal hydrophobic segment and that the sequences are incomplete at the 5'-region. The studies indicated that C-type lectin-related proteins are also derived from the amino terminal region of these precursors. Based on these findings, a five-domain structure is proposed for the precursors.