Sugar-binding site of ERGIC-53.

Omit Fo–Fc electron density map of α2-Man2 contoured at 2.0 σ. Additional electron densities flank the Manα1,2-Man moiety occupying the primary binding sites (sites 2 and 3), suggesting two alternative binding modes: (A) mode I and (B) mode II. The mannose residue occupying site 1 was modeled by superimposing the reducing-terminal mannose residue of the α2-Man2 ligand in the VIP36 crystal structure (PDB code: 2DUR) [30], which has a highest resolution (1.65 Å) among the L-type lectin-sugar complexes so far reported, while the modeling of the mannose residue accommodated in site 4 was based on the crystal structure of the non-reducing-terminal mannose residue of α2-Man2 bound in ERGIC-53 (PDB code: 4GKX) [31].