*3.2. Disaccharides*

The PDB dataset consisting of 105 proteins-GAG complexes contains 270 disaccharides [9]. Table 1 displays the major disaccharides as extracted from GAG-DB.


**Table 1.** Major disaccharides found in the GAG-protein complexes.

Such a rich set of experimental data provides useful information to validate and improve computational strategies to build GAG models. The determination of the conformational preferences of GAG disaccharides can be assessed by computing potential energy surfaces as a function of their glycosidic torsion angles Φ and Ψ as implemented in the CAT application [70]. As an example, Figure 7 displays two such potential energy surfaces (alternatives are not shown). In all cases, the experimentally observed Φ and Ψ are plotted on the corresponding potential energy surfaces. While being somehow scattered, they are all located on the lowest energy basins. 

Φ Ψ **Figure 7.** Φ and Ψ angles measured in the 3D structures of cocrystallized GAG protein complexes, reported on conformational maps.

Similar features are observed for all disaccharides (or disaccharide units) irrespective of the presence and the positions of sulfate groups on the monosaccharides. The agreement between the repertoire of the experimentally determined conformations and those predicted by computational methods provided the basis to develop a pipeline to translate glycosaminoglycans sequences into 3D models (http://glycan-builder.cermav.cnrs.fr/gag/) [47].
