Expression of a single βα chain protein of equine LH/CG in milk of transgenic rabbits and its biological activity

Equine chorionic gonadotropin (eCG) is a heavily glycosylated glycoprotein composed of non-covalently linked alpha- and beta -subunits. eCG possesses the particularity to bind to both LH and FSH receptors in species other than horses and to have a prolonged plasma half-life. All these properties make it of utmost interest for livestock fertilization program. Up to now, the only source of eCG is the serum of pregnant mare. Rabbit mammary gland is considered as a system able to produce recombinant glycoproteins in sufficient quantity for pharmaceutical use. Here we described the production of a recombinant single beta alpha chain of eLH/CG in the milk of transgenic rabbit. The construction of a single-chain permits to by-pass the problem of association-dissociation of the subunits. This recombinant hormone is greatly expressed (21.7 mg/l) and presents similar in vitro LH and FSH bioactivities. However, B alpha eLH/CG shows an extremely rapid clearance (approximate to 10 min), which could explain the absence of in vivo biological activity. So the rabbit mammary gland is not appropriate Tor the production of a recombinant active eLH/CG. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.