The glycoprotein hormone family: Structure and function of the carbohydrate chains

This chapter discusses the structure and function of the carbohydrate chains of the glycoprotein hormone family. The family of glycoprotein hormones consists of lutropin (LH), follitropin (FSH), and thyrotropin (TSH) synthesized in the anterior pituitary and chorionic gonadotropin which is synthesized only in the placenta of human, primate, and equine. The hormones are heterodimers composed of two non-covalently joined α and β subunits. Both subunits are glycosylated and contain N- and, in the case of the CGβ subunit, O-linked oligosaccharides which account for 15-40% of their mass. Assembly of the common α subunit, with any of the four β subunits, results in unique properties of each hormone that are reflected in binding to hormone-specific receptors and subsequent signal transduction. Gonadotropins regulate reproductive functions; LH stimulates steroidogenesis in ovarian granulosa and theca cells, and testicular Leydig cells. One function of hCG is to maintain high progesterone production in the corpus luteum to maintain pregnancy and hCG and LH bind to the same receptor.