DIFFERENTIAL SECRETION AND GLYCOSYLATION OF RECOMBINANT HUMAN CHORIONIC-GONADOTROPIN (BETA-HCG) SYNTHESIZED USING DIFFERENT PROMOTERS IN THE BACULOVIRUS EXPRESSION VECTOR SYSTEM

Recombinant baculoviruses vAcbetahCG(COR) and vAcbetahCG(POL), carryin g the gene (betahCG) encoding the beta-subunit of human chorionic gona dotropin under the transcriptional control of the late AcNPV core prot ein gene promoter (P(COR)) and the very late polyhedrin gene promoter (P(POL)), respectively, were constructed and used to infect lepidopter an cells. Western blot analysis of intra- and extracellular recombinan t betahCG (re-betahCG) revealed that the secretion of betahCG(COR) was relatively higher. Enzymatic and chemical analysis of carbohydrates s howed that betahCG(COR) was more glycosylated than betahCG(POL). Howev er, the insect-derived betahCG, with a high-mannose type of sugar, was glycosylated differently and to a lesser extent when compared with th e native, urinary betahCG, and consequently, betahCG(COR) was more bio active on a unit-mass basis than betahCG(POL). This temporal gene expr ession strategy, besides being able to circumvent the 'secretory load' encountered during the synthesis of extensively glycosylated proteins in the baculovirus system, also offers a model to study the role of c arbohydrates, both in qualitative and quantitative terms, in protein s tructure and function.