Top, Ribbon diagram of the MRH domains of S. pombe GIIβ (orange, solution structure, PDB ID: 2LVX), human OS-9 (gray, crystal structure, PDB ID: 3AIH), bovine CD-MPR (magenta, crystal structure, PDB ID: 1C39), bovine CI-MPR MRH domain 3 (green, crystal structure, PDB ID: 1SZO), bovine CI-MPR MRH domain 5 (blue, solution structure, PDB ID: 2KVB). Disulfide bridges are shown in yellow, N and C termini are boxed, β-strands are numbered from the N to C terminus, and loops C and D are labeled. Bottom, Close-up view of the carbohydrate binding sites are shown below the respective ribbon diagram. The four essential residues for mannose binding are shown along with the proposed linkage-sensing Tyr or Trp. Molecular surfaces are shown in gray over the ribbon diagram. Carbohydrate ligands are depicted as ball-and-stick. Structures solved in the presence of a bound ligand (Manα1,6Manα1,6Man for OS-9, pentamannosyl phosphate for CD-MPR, M6P for CI-MPR MRH domain 3) are shown in yellow. Modeled ligands are depicted in gray (mannose for GIIβ, methyl-M6P-GlcNAc for CI-MPR MRH domain 5) and are placed in the binding pocket based on superimposition of the four essential residues with a known MRH domain structure containing a bound ligand.