Thromb Haemost 2005; 93(03): 420-429
DOI: 10.1160/TH04-11-0707
Blood Coagulation, Fibrinolysis and Cellular Haemostasis
Schattauer GmbH

Gene duplication of coagulation factor V and origin of venom prothrombin activator in Pseudonaja textilis snake

Thi Nguyet Minh Le
1   Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Republic of Singapore
,
Md Abu Reza
1   Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Republic of Singapore
,
Sanjay Swarup
1   Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Republic of Singapore
,
R. Manjunatha Kini
1   Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Republic of Singapore
2   Department of Biochemistry and Molecular Biophysics, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia, USA
› Author Affiliations

Financial support: This work was supported by Academic research grants from the National University of Singapore, Singapore.
Further Information

Publication History

Received 02 November 2004

Accepted after revision 10 February 2004

Publication Date:
14 December 2017 (online)

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Summary

The origin and evolution of venom toxins is a mystery that has evoked much interest. We have recently shown that pseutarin C, a prothrombin activator from Pseudonaja textilis venom, is structurally and functionally similar to mammalian coagulation factor Xa – factor Va complex. Its catalytic subunit is homologous to factor Xa while the nonenzymatic subunit is homologous to factor Va. P.textilis therefore has two parallel prothrombin activator systems: one expressed in its venom gland as a toxin and the other expressed in its liver and released into its plasma as a haemostatic factor. Here we report the complete amino acid sequence of factor V (FV) from its liver determined by cDNA cloning and sequencing. The liver FV shows 96% identity to pseutarin C nonenzymatic subunit. Most of the functional sites involved in its interaction with factor Xa and prothrombin are conserved. However, many potential sites of post-translational modifications and one critical cleavage site for activated protein C are different. The absence of the latter cleavage site makes pseutarin C nonenzymatic subunit resistant to inactivation and enhances its potential as an excellent toxin. By PCR and real-time quantitative analysis, we show that pseutarin C nonenzymatic subunit gene is expressed specifically in the venom gland at ~280 fold higher than that of FV gene in liver. These two are thus encoded by two separate genes that express in a highly tissue-specific manner. Our results imply that the gene encoding pseutarin C nonenzymatic subunit was derived by the duplication of plasma FV gene and they have evolved to perform distinct functions.