A Single-Chain Tetradomain Glycoprotein Hormone Analog Elicits Multiple Hormone Activities In Vivo

Abstract We previously demonstrated that genetically linking one or more of the glycoprotein hormone-specific β subunit genes to the common α subunit resulted in single-chain analogues that were bioactive in vitro. The ability of such large structures to bind their cognate receptors with high affinity supported the hypothesis that extensive flexibility exists between the ligand and receptor to establish a functional complex. To further characterize the extent of this conformational flexibility, we engineered a single-chain analogue that consists of sequentially linked thyroid-stimulating hormone (TSH) β, follicle-stimulating hormone (FSH) β, and chorionic gonadotropin (CG) β subunits to the α subunit and expressed this chimera in transfected CHO (Chinese hamster ovary) cells. Because the four subunits are genetically linked and expressed as a single-chain, this analogue presumably lacks significant native structural features of the individual heterodimers. However, it exhibited FSH, CG, and TSH activities...