<p>G-protein-coupled receptors, GPCRs, constitute a vast protein family that encompasses a wide range of functions (including various autocrine, paracrine and endocrine processes). They show considerable diversity at the sequence level, on the basis of which they can be separated into distinct groups. We use the term clan to describe the GPCRs, as they embrace a group of families for which there are indications of evolutionary relationship, but between which there is no statistically significant similarity in sequence [<cite idref="PUB00004961"/>]. The currently known clan members include the rhodopsin-like GPCRs, the secretin-like GPCRs, the cAMP receptors, the fungal mating pheromone receptors, and the metabotropic glutamate receptor family. There is a specialised database for GPCRs (http://www.gpcr.org/7tm/). </p><p>The rhodopsin-like GPCRs themselves represent a widespread protein family that includes hormone, neurotransmitter and light receptors, all of which transduce extracellular signals through interaction with guanine nucleotide-binding (G) proteins. Although their activating ligands vary widely in structure and character, the amino acid sequences of the receptors are very similar and are believed to adopt a common structural framework comprising 7transmembrane (TM) helices [<cite idref="PUB00000131"/>, <cite idref="PUB00002477"/>, <cite idref="PUB00004960"/>].</p><p>The gonadotrophins (luteinising hormone, choriogonadotrophin, follicle-stimulating hormone) and thyroid-stimulating hormone are heterotrimericglycoproteins composed of a common alpha-subunit and distinct beta-subunits. The carbohydrate moiety of the glycoproteins has an essential role in receptor recognition. The receptors share close sequence similarity, and are characterised by large extracellular domains believed to be involved in hormone binding via leucine-rich repeats (LRR) [<cite idref="PUB00005254"/>]. Modelling of this portion of the receptors suggests that they contain three-dimensional structures similar to that of <taxon tax_id="9823">Sus scrofa</taxon> (Pig) ribonuclease inhibitor [<cite idref="PUB00005254"/>].</p><p>FSH is released from the anterior pituitary under the influence ofgonadotrophin-releasing hormone and oestrogens, and from the placenta duringpregnancy. In females, it acts on the ovaries, promoting developmentof follicles and is the principal hormone regulating secretion ofoestrogens. In males, it is responsible for the integrity of theseminiferous tubules and acts on Sertoli cells to support gametogenesis.FSH is used clinically to treat infertility in females and for some typesof spermatogenesis in males. The receptor is found in ovary and testis,its predominant effector pathway being via activation of adenylyl cyclasethrough G proteins.</p> Follicle-stimulating hormone receptor