INSECT CELLS INFECTED WITH A RECOMBINANT BACULOVIRUS EXPRESS BOTH O- AND N-GLYCOSYLATED FORMS OF THE RAT GLYCOPROTEIN HORMONE ALPHA -SUBUNIT

: Glycoprotein hormones LH, FSH, TSH and chorionic gonadotrophin are heterodimers composed of two non-covalently associated subunits, a common alpha- and a specific beta-subunit. A recombinant baculovirus containing a cDNA encoding the alpha-subunit of rat glycoprotein hormones was constructed. Viral-infected cells expressed, 48 h post infection, 7-10 mg immunoreactive alpha-glycopolypeptide/6 x 10(8) cells, of which 65-6% was able to associate with native LH beta and formed a biologically active heterodimeric hormone that bound to testicular receptors. The treatment with specific glycanases showed that the recombinant alpha-subunit was produced as two differently glycosylated forms; an M(r) 23 000 form which contained exclusively N-linked carbohydrate units and another of M(r) 25 000 which appeared to contain additional 0-linked carbohydrate. Data demonstrated that the alpha-subunit was expressed by insect cells in a manner similar to that by mammalian pituitary gonadotropes producing both the N- and O-glycosylated forms although only the N-glycosylated alpha-subunit is known to be capable of associating with the beta-subunit.