Isolation and characterization of anticoagulant protein from the venom of Hemachatus haemachatus (African Ringhals Cobra)

Abstract

Two synergistically acting anticoagulant three-finger proteins, hemextin A and hemextin B were purified from the venom of the elapid Hemachatus haemachatus (African Ringhals cobra). Hemextin A, but not B has mild anticoagulant activity. However, hemextin B forms a tetrameric complex (hemextin AB complex) with hemextin A and enhances its anticoagulant potency. Anticoagulation is mediated by the specific inhibition of coagulation factor VIIa (the serine protease involved in clot initiation), by binding to its heavy chain. Hemextin AB complex is the only known heterotetrameric complex of three-finger toxins and also the only known specific inhibitor of FVIIa, for the inhibition of which it does not use tissue-factor or factor X/Xa as scaffold. Biophysical studies show that the complex is stabilized by the participation of both electrostatic and hydrophobic interaction and its formation is enthalpically driven. This study therefore provides a new paradigm in the search for anticoagulants to treat thromboembolic disorders.