The Activation of Plasma Factor XIII with the Snake Venom Enzymes Ancrod and Batroxobin Marajoensis

New Insights on Moojase, a Thrombin-Like Serine Protease from Bothrops moojeni Snake Venom

Snake venom serine proteases (SVSPs) are enzymes that are capable of interfering in various parts of the blood coagulation cascade, which makes them interesting candidates for the development of new therapeutic drugs. Herein, we isolated and characterized Moojase, a potent coagulant enzyme from Bothrops moojeni snake venom. The toxin was isolated from the crude venom using a two-step chromatographic procedure. Moojase is a glycoprotein with N-linked glycans, molecular mass of 30.3 kDa and acidic character (pI 5.80⁻6.88). Sequencing of Moojase indicated that it is an isoform of Batroxobin. Moojase was able to clot platelet-poor plasma and fibrinogen solutions in a dose-dependent manner, indicating thrombin-like properties. Moojase also rapidly induced the proteolysis of the Aα chains of human fibrinogen, followed by the degradation of the Bβ chains after extended periods of incubation, and these effects were inhibited by PMSF, SDS and DTT, but not by benzamidine or EDTA. RP-HPLC analysis of its fibrinogenolysis confirmed the main generation of fibrinopeptide A. Moojase also induced the fibrinolysis of fibrin clots formed in vitro, and the aggregation of washed platelets, as well as significant amidolytic activity on substrates for thrombin, plasma kallikrein, factor Xia, and factor XIIa. Furthermore, thermofluor analyses and the esterase activity of Moojase demonstrated its very high stability at different pH buffers and temperatures. Thus, studies such as this for Moojase should increase knowledge on SVSPs, allowing their bioprospection as valuable prototypes in the development of new drugs, or as biotechnological tools.

Factor XIII: a coagulation factor with multiple plasmatic and cellular functions

Factor XIII (FXIII) is unique among clotting factors for a number of reasons: 1) it is a protransglutaminase, which becomes activated in the last stage of coagulation; 2) it works on an insoluble substrate; 3) its potentially active subunit is also present in the cytoplasm of platelets, monocytes, monocyte-derived macrophages, dendritic cells, chondrocytes, osteoblasts, and osteocytes; and 4) in addition to its contribution to hemostasis, it has multiple extra- and intracellular functions. This review gives a general overview on the structure and activation of FXIII as well as on the biochemical function and downregulation of activated FXIII with emphasis on new developments in the last decade. New aspects of the traditional functions of FXIII, stabilization of fibrin clot, and protection of fibrin against fibrinolysis are summarized. The role of FXIII in maintaining pregnancy, its contribution to the wound healing process, and its proangiogenic function are reviewed in details. Special attention is given to new, less explored, but promising fields of FXIII research that include inhibition of vascular permeability, cardioprotection, and its role in cartilage and bone development. FXIII is also considered as an intracellular enzyme; a separate section is devoted to its intracellular activation, intracellular action, and involvement in platelet, monocyte/macrophage, and dendritic cell functions.

On the occurrence of thrombin-like enzymes in mosquitoes

A thrombin-like enzyme has been identified in mosquitoes and partially purified. The enzyme preparation displays on SDS gel electrophoresis a major protein band of about 22 kDa and one minor of about 28 kDa. The enzyme preparation cleaves a synthetic substrate (S-2238) for thrombin with Km 113 mumol/L (as compared to 3 mumol/L for thrombin). The enzyme clots fibrinogen and plasma. During activation of fibrinogen, fibrinopeptide A (but scarcely fibrinopeptide B) is released. The enzyme is not inhibited by hirudin and activates (if at all) factor XIII differently from thrombin. Predominantly gamma-dimers are formed in the cross linking process. As compared to thrombin a larger extent of activation is required to induce gelation (clotting) by the mosquito enzyme. At a given clotting time the enzyme produces tighter gel structures than thrombin. In its action the enzyme resembles the snake venom enzyme, batroxobin.

Ancrod for the treatment of acute ischemic brain infarction. The Ancrod Stroke Study Investigators

BACKGROUND AND PURPOSE

There is no acute therapy proven to be of benefit for ischemic stroke. Ancrod is a potentially effective therapy because of the advantageous consequences of fibrinogen lowering.

METHODS

We studied the safety and efficacy of ancrod in patients with acute ischemic stroke administered within 6 hours of stroke onset. In a double-blind, randomized, placebo-controlled trial 64 patients received intravenous ancrod and 68 received placebo for 7 days. Neurological outcome, disability, and brain infarct volume were measured.

RESULTS

There was no significant difference in overall mean scores on the Scandinavian Stroke Scale. No increase in bleeding occurred in the ancrod-treated patients. The target reduction of plasma fibrinogen levels of less than 100 mg/dL was achieved in only 15 (23%) of 64 ancrod-treated patients. Those patients with ancrod-induced 6-hour fibrinogen levels 130 mg/dL or less had a marginally significantly better neurological outcome on the Scandinavian Stroke Scale, mortality, and Barthel Index than ancrod-treated patients with higher fibrinogen levels.

CONCLUSIONS

Ancrod appears safe and potentially effective when administered to patients within 6 hours of onset of ischemic stroke.

Fragmentation of actin by thrombin-like snake venom proteases

The effect of thrombin-like snake venom proteases (Ancrod of Agkistrodon rhodostoma and Batroxobins of Bothrops moojeni and Bothrops marajoensis) on skeletal muscle actin was studied and compared to the thrombic cleavage of this protein. Only EDTA-pretreated G- and F-actin were split by thrombin and Ancrod, while Batroxobins hydrolyzed native G-actin, too. The time course of digestion was followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. A split product of 37 500 daltons appeared first which was cleaved further resulting in three lower molecular weight fragments. The sodium dodecyl sulfate gel pattern of thrombic fragmentation was well distinguishable from those caused by Ancrod and Batroxobins. The first split products of Batroxobin digestion--a smaller peptide and the 37 500 dalton fragment--were isolated and by estimating their N-, and C-terminal end groups and amino acid compositions the peptide bond hydrolyzed first was located in the primary structure of actin. It was established that while thrombin split off two actino-peptides (at Arg(28)-Ala(29) and Arg(39)-His(40) from the N-terminal end of the molecule only Arg(39)-His(40) was cleaved by Batroxobins.