Crystal structures of RbmC2 with mannotriose and GlcNAc-Man bound.

(A) Crystal structure of the isolated RbmC2 β-prism domain with mannotriose (1,3-α-1,6-α-D-mannotriose) shown in stick representation. The mannotriose core in a typical complex N-glycan is boxed (lower left, see key in Fig 2A). A simulated annealing OMIT electron density map contoured to 2.5 σ for the ligand is displayed in blue mesh, duplicated and extracted from the overall structure for clarity (lower right). (B) Stereo view of residues that directly interact with the mannotriose ligand. Putative hydrogen bonds are displayed as blue dotted lines and van der Waals contacts are denoted with a semi-transparent surface representation. Within the mannotriose ligand (green sticks), the attachment point of connecting saccharides in an intact complex N-glycan are colored yellow. A water molecule (B-factor = 4.18 Ų) (blue sphere) is held in a tetrahedral coordination sphere involving N871, W948, and two hydroxyl groups from the mannotriose glycan fragment. (C) Same as in A, but showing the GlcNAc-Man-bound structure, solved to 1.8 Å resolution. (D) Same as in B, but for the GlcNAc-Man structure.