A plant oleosin was used as a 'carrier' for the production of the leech anticoagulant protein, hirudin (variant 2). The oleosin-hirudin fusion protein was expressed and accumulated in seeds. Seed-specific expression of the oleosin-hirudin fusion mRNA was directed via an Arabidopsis oleosin promoter. The fusion protein was correctly targeted to the oil body membrane and separated from the majority of other seed proteins by flotation centrifugation. Recombinant hirudin was localized to the surface of oil bodies as determined by immunofluorescent techniques. The oleosin-hirudin fusion protein accumulated to ca. 1% of the total seed protein. Hirudin was released from the surface of the oil bodies using endoprotease treatment. Recombinant hirudin was partially purified through anion exchange chromatography and reverse-phase chromatography. Hirudin activity, measured in anti-thrombin units (ATU), was observed in seed oil body extracts, but only after the proteolytic release of hirudin from its oleosin 'carrier'. About 0.55 ATU per milligram of oil body protein was detected in cleaved oil body preparations. This activity demonstrated linear dose dependence. The oleosin fusion protein system provides a unique route for the large-scale production of recombinant proteins in plants, as well as an efficient process for purification of the desired polypeptide.

The advantages and limitations of plant‐based systems for the production of recombinant biopharmaceutical proteins are discussed in the context of other host production systems presently available. A novel approach for the purification of recombinant proteins expressed in oilseeds is described that is based on the targeting of these proteins to seed oil bodies. The utility of this approach is demonstrated by the purification of the anticoagulant protein hirudin, produced in seeds of Brassica napus. Drug Dev. Res. 42:172–181, 1997. © 1997 Wiley‐Liss, Inc.

Hirudin, a blood anticoagulant protein from leeches, and β-glucuronidase were produced in Brassica carinata Braun (Ethiopian mustard) seeds using oleosin as a carrier. Cotyledonary petioles were infected with Agrobacterium strains containing oleosin-glucuronidase (pCGNOBPGUS-A) or oleosin-hirudin (pCGN-OBHIRT) constructs. Polymerase chain reaction and neomycin phosphotransferase II enzyme assays confirmed the presence of the fusion genes in plants regenerating under selection. The fusion polypeptides were correctly expressed and targeted to the oil-bodies of the seeds with high fidelity (ca. 90%). Recombinant protein was purified from all other cellular protein by a simple flotation process and cleaved from oil-bodies using the endoprotease, Factor Xa. Hirudin activity was measured using a colorimetric thrombin inhibition assay and an activity in the range of 0.2-0.4 antithrombin units per milligram of oil-body protein was detected. B. carinata offers an attractive alternative for the production of recombinant proteins using oleosin technology.

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