Figure 8.

GlcNAc–Asn linkages in the two energy minima as found in the AfβG structure. (a) Stereoview of all superposed GlcNAc–Asn sites for chain A. For clarity reasons, Asn residues in other rotamer forms are omitted, and only one representative GlcNAc is shown for the two conformations (1101, with blue C atoms, and 1401, with yellow C atoms). (b) Nag1101–Asn253 as a representative of the most frequent, lowest-energy linkage conformation. (c) Nag1401–Asn443 in the secondary energy minimum described by Imberty & Perez (1995 ▸), with Trp431 taking part in CH–π stacking interactions with the apolar face of Nag1401. The electron-density maps shown here were calculated from 2mF _o − DF _c coefficients and contoured at 2σ. As they both show similar values (∼180°), ψ_N torsions are not depicted in (b) and (c).