Figure 4

The three dimensional structure of hCG [4]. In order to form crystals hCG was first deglycosylated. hCG and hyperglycosylated hCG have identical amino acid sequence [1], yet vary in function. hCG binds the hCG/LH receptor while hyperglycosylated hCG antagonizes a TGFß receptor [6–8]. As such the glycosylation (all removed) has to make a structural difference to the two hCG forms. This difference is not shown. Oligosaccharide are added to the three dimensional structure assuming the carbohydrate structure observation of Elliott et al. [1]. Oligosaccharides are charged so must project towards the surface of the molecule. L in oligosaccharides is N-acetylgalactosamine, A is N-acetylglucosamine, S is sialic acid or N-acetyl-neuraminic acid, G is galactose, M is mannose and F is fucose.