A molecule acclaimed as "the mother of all proteins" will bemanufactured in the mammary glands of sheep.Donna Prunkard, a Scientist at Zymogenetics Inc., of Seattle, broke thenews on Friday at the 13th International Fibrinogen Workshop, inManchester, U.K. She told the last session on the last day of themeeting that Pharmaceutical Proteins Ltd. (PPL), of Edinburgh, hadextracted human fibrinogen in high volume from the milk of micerendered transgenic with genes _ supplied by Zymogenetics _ thatencoded the protein.PPL plans to transfect the fibrinogen gene into fertilized ovineembryos, targeted to express the protein expressly in the milk-secretingcells of progeny ewes. The Scottish company pioneered protein-yielding livestock with its herd of transgenic sheep carrying humanalpha-1-antitrypsin in their milk.Fibrinogen, Factor I in the blood-coagulating cascade, is clipped bythrombin to form fibrin, the meshwork of a clot. This is cross-linked byFactor XIII to strengthen the clot.Fibrinogen is also a high-value commercial molecule, PPL's managerof new business development, molecular biologist Erica Whittaker, toldBioWorld Today. "Special surgical tissue sealants that have fibrinogenas the main component are made by three companies in the world," shenoted. "They are Immuno AG of Austria, Hoechst of Germany andFujisawa, Japan. The fibrinogen is extracted from pooled donor-bloodplasma, and sold in Germany, Belgium, Italy and Japan."Potential Multi-Million Market For Sticky ProteinMark Murray, Zymogenetics' senior director of new businessdevelopment, said that that world market for the surgical glue rangesbetween $50 million and $80 million a year. In the U.S., he toldBioWorld Today, where the European product is not approved for use,some surgeons make their own "autologous sealant" from the blood ofpre-operative patients. The tissue-adhesive's uses include proceduressuch as cardiology, otolaryngology and plastic surgery, where suturesor staples are not appropriate, .Zymogenetics, which is wholly owned by Novo Nordisk of Bagsvaard,Denmark, has a long-standing collaborative research arrangement withPPL. The Danish company, Murray said, is the world's largestproducer of recombinant proteins."They provided the gene," Whittaker said; "we did the transgenic workwith the mice. Together, we performed the protein analysis, todetermine if the molecule is properly assembled and folded,concentrated, and bioactive."The Scottish firm has "over a dozen mice with fibrinogen in theirmilk," she said; "It worked very well."Specifically, the mouse milk yielded about one gram per liter of fluid."This is several hundred-fold greater than levels that have beenachieved by conventional and culture production methods," Murraysaid, adding, "and we expect similar or better levels from sheep milk.""We're not talking about milligrams, but grams per liter," Whittakersaid, "which shows how powerful the technology is. Scientists here andin Seattle have really been walking on air about this achievement.One's expectations weren't really very high, because fibrinogen isbasically the most complex protein known to man. That's whyZymogenetics' director of cellular and molecular biology, Don Foster,called it the mother of all proteins."The molecule is a hexamer, consisting of three dimeric, sulfide-bondedchains, alpha, beta and gamma. Its mass is approximately 340kilodaltons. Zymogenetics isolated its three genes, one per chain, fromgenomic, not cDNA, constructs.Anti-Emphysema Trials In OffingIt's the second protein of interest that PPL has made public, but notsecond in priority, of "about a dozen in the firm's product pipeline,"Whittaker vouchsafed.Meanwhile, PPL's maiden milk-borne molecule, alpha-1-antitrypsin, aputative emphysema drug, is edging toward clinical trials. "Thecommercial production flock is being developed," Whittaker said, "andthere's already a flock of over 100 transgenic ewes up and running,producing material for preclinical animal trials. We'll begin these nextyear, probably in Britain, in conjunction with Bayer AG of Germany."PPL's basic enabling technology is embodied in U.S. patent No.5,322,775, issued June 21, 1994. Its core claim, said Ron James, thecompany's managing director, "involved the isolation of the milk beta-lactoglobulin (BLG) gene promoter, and its use to target expression ofintroduced genes only in the mammary gland of transgenic livestock."He added: "We are using the BLG promoter to produce for our partnersa range of proteins, in the milk of such animals, all of which havepotentially important therapeutic uses."Murray said that Zymogenetics and PPL have a range of such newproducts in the works. n
-- David N. Leff Science Editor
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