Orientation of sugars bound to the principal C-type carbohydrate-recognition domain of the macrophage mannose receptor.
The extracellular region of the macrophage mannose receptor, a protein involved in the innate immune response, contains eight C-type carbohydrate-recognition domains (CRDs). The fourth of these domains, CRD-4, is central to ligand binding by the receptor, and binds mannose, fucose and N-acetylglucosamine by direct ligation to Ca2+. Site-directed mutagenesis combined with NMR and molecular modelling have been used to determine the orientation of monosaccharides bound to CRD-4. Two resonances in the 1H NMR spectrum of CRD-4 that are perturbed on sugar binding are identified as a methyl proton from a leucine side chain in the core of the domain and the H-2 proton of a histidine close to the predicted sugar-binding site. The effects of mutagenesis of this histidine residue, a nearby isoleucine residue and a tyrosine residue previously shown to stack against sugars bound to CRD-4 show the absolute orientation of sugars in the binding site. N-Acetylglucosamine binds to CRD-4 of the mannose receptor in the orientation seen in crystal structures of the CRD of rat liver mannose-binding protein. Mannose binds to CRD-4 in the orientation seen in the CRD of rat serum mannose-binding protein and is rotated by 180 degrees relative to GlcNAc bound to CRD-4. Interaction of the O-methyl group and C-1 of alpha-methyl Fuc with the tyrosine residue accounts for the strong preference of CRD-4 for this anomer of fucose. Both anomers of fucose bind to CRD-4 in the orientation seen in rat liver mannose-binding protein.
Hitchen
P G
PG
Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
Mullin
N P
NP
Taylor
M E
ME
D000117:Acetylglucosamine / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002236:Carbohydrate Conformation; D005643:Fucose / Q000031:analogs & derivatives / Q000378:metabolism; D037181:Lectins, C-Type; D008264:Macrophages / Q000378:metabolism / Q000648:ultrastructure*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008358:Mannose / Q000378:metabolism; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D009005:Monosaccharides / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013379:Substrate Specificity
D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D009005:Monosaccharides; D011956:Receptors, Cell Surface; D005643:Fucose; C076754:2-O-methylfucose; D008358:Mannose; D000117:Acetylglucosamine