Molecular Basis of the Specificity of Binding of Glycoprotein Hormones to Their Receptors

Introduction

THREE glycoprotein hormones are synthesized and secreted by the pituitary under hypothalamic control. Two of them are the gonadotropins, LH and FSH, and the third one is TSH. During gestation in primates and equidaes an additional gonadotropin, CG, is secreted by the placenta.

Pituitary gonadotropins play pivotal roles in the control of reproductive function in both the female (1, 2) and the male (3) while the main role of TSH is in the control of thyroid gland activity (4). Although the human (h) and equine (e) CGs (the latter previously named PMSG) have been studied extensively, the full extent of their roles remains equivocal (5, 6).

Glycoprotein hormones form a family of structurally related molecules that are among the most complex molecules possessing hormonal activities. Despite their extensive homologies, these hormones exhibit high specificities, indispensable for their respective and often coordinated physiological roles. The present review is an attempt to summarize and interpret the available data concerning the molecular basis for their highly specific interaction with their receptors.