the three - dimensional structure of human chorionic gonadotrophin has been determined by x - ray crystallography and the coordinates of the individual atoms are presented . analogues of hcg and other glycoprotein hormones sharing a similar α - subunit structure are produced by inputting chemical changes to the structure into a computer loaded with three - dimensional molecular simulation software and representing visually on a computer display . the three - dimensional structures of the original glycoprotein and the chemically modified analogues are compared , and those analogues wherein the three - dimensional configuration and spatial arrangement of regions involved in receptor binding and signal transduction remain substantially preserved are selected for synthesis by molecular biology techniques and screening for biological activity . glycoprotein analogues with additional glycosylation sites , and deletion of non - essential hairpins are disclosed .