Figure 6.

(a) View of an O-glycan. This shows one of the rare examples of O-glycosylation found in the PDB (code 4a5t, solved to 3.49 Å resolution), reported by Xue et al. (2012 ▸). As can be seen from the two-dimensional diagram (see b), the GalNAc–Thr linkage was originally modelled as β whilst in reality it had to be α. It is only by using all available knowledge of glycochemistry that these mistakes can be avoided, as the fit to a featureless map must always be tightly restrained to what is known in terms of link distances, angles and torsions. (b) Two-dimensional representation by Privateer. The dashed line indicates an α-link.