CRYSTAL-STRUCTURE OF HUMAN CHORIONIC-GONADOTROPIN

The three-dimensional structure of human chorionic gonadotropin shows that each of its two different subunits has a similar topology, with t hree disulphide bonds forming a cystine knot. This same folding motif Is found in some protein growth factors. The heterodimer is stabilized by a segment of the beta-subunit which wraps around the alpha-subunit and is covalently linked like a seat belt by the disulphide Cys 26-Cy s 110. This extraordinary feature appears to be essential not only for the association of these heterodimers but also for receptor binding b y the glycoprotein hormones.