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Bothrojaracin is a potent and selective thrombin inhibitor that has been
isolated from the venom of Bothrops jararaca. It does not interact with the
catalytic site of the enzyme but binds to both anion-binding exosites 1 and 2
resulting in a potent inhibition of thrombin activity towards fibrinogen and
platelets [Zingali, R. B., Jandrot-Perrus, M., Guillin, M. C. & Bon, C.
(1993) Biochemistry 32, 10794-108021. Bothrojaracin is a 27-kDa protein composed
of two disulfide-linked polypeptide chains, A and B, of 15 kDa and 13 kDa,
respectively. The sequences of A and B chains determined by molecular cloning
exhibit a high degree of identity with other snake venom lectin-like proteins.
In contrast to other ligands that interact with thrombin exosite 1, the amino
acid sequence of bothrojaracin does not contain an acidic sequence similar to
the C-terminal tail of hirudin. Expression of functional bothrojaracin was
achieved in COS cells upon transfection with two pcDNA3 vectors containing the
complete cDNAs. Recombinant bothrojaracin, which was secreted into the medium,
was able to bind to and inhibit thrombin. When expressed alone, the B chain
formed inactive dimers that were secreted into the culture medium. In contrast,
no bothrojaracin-related protein was detected in conditioned media from cells
transfected with the A chain.
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