PMID: 8202136
Lapthorn AJ, Harris DC, Littlejohn A, Lustbader JW, Canfield RE, Machin KJ, Morgan FJ, Isaacs NW
Crystal structure of human chorionic gonadotropin.
Nature. 1994 Jun 9;369(6480):455-61.
The three-dimensional structure of human chorionic gonadotropin shows that each of its two different subunits has a similar topology, with three 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-Cys 110. This extraordinary feature appears to be essential not only for the association of these heterodimers but also for receptor binding by the glycoprotein hormones.