| Type: | Conserved_site | Name: | Gonadotropin, beta subunit, conserved site |
| Description: | The crystal structures of four growth factors; nerve growth factor, transforming growth factor-beta, platelet-derived growth factor, and human chorionic gonadotropin from four separate superfamilies revealed that these proteins are structurally related and share a common overall topology []. These proteins show very little sequence homology, but they all have an unusual arrangement of six cysteines linked to form a "cystine-knot" conformation. The active forms of these proteins are dimers, either homo- or heterodimers []. Because of their shape, there appears to be an intrinsic requirement for the cystine-knot growth factors to form dimers. This extra level of organisation increases the variety of structures built around this simple structural motif [].Glycoprotein hormones [, ] (or gonadotropins) are a family of proteins which include the mammalian hormones follitropin (FSH), lutropin (LSH), thyrotropin (TSH) and chorionic gonadotropin (CG), as well as at least two forms of fish gonadotropins. All these hormones consist of two glycosylated chains (alpha and beta). In mammalian gonadotropins, the alpha chain is identical in the four types of hormones but the beta chains, while homologous, are different.The beta chains are proteins of about 100 to 140 amino acid residues which contain the cysteine-knot domain [], as shown in the following schematic representation.+----------------------+ | +------------|-----------------------------+| +-|------------|--------+ | | | | | | |xxxCxxxxxxxCxCxxCxCxxxxxxxCxxxxxxxxCxxxxxxxCxCxCxxCxxxxxCxxxxxxxxxxx | | | | | || | | | +--+ +-|------------------------+ |+--------------------------+ 'C': conserved cysteine involved in a disulphide bond. | Short Name: | Gonadotropin_bsu_CS |
