Production of hirudin (an anticoagulant) for thrombosis
Hirudin is another important drug that is used as anticoagulant for treatment of thrombosis. It was originally isolated from the leech (Hirudo medicinalis), but is now mostly produced by recombinant bacteria and yeast. Transgenic plants (oilseed rape, tobacco and Ethiopian mustard) were initially produced, which although expressed hirudin, but purification of hirudin from the seed proved rather expensive. It has been shown that hirudin in transgenic plants can be produced as a fusion protein with oleosin, which is transported to oil bodies thus making the purification cheaper and easier (oleosin­hirudin fusion proteins are extracted with oil bodies and can be easily separated by flotation centrifugation). Between the two genes (for hirudin and oleosin), the fusion gene also contained a sequence that encoded an endopeptidase recognition site, thus enabling easy cleavage of the fusion protein releasing hirudin from oleos in-hirudin fusion protein. This strategy also ensures that hirudin becomes active only after extraction, thus reducing environmental risks, if any. Transgenic oilseed rape expressing hirudin is now commercially grown by SemBiosys in Calgary (Canada).