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Original Article |
Correspondence to: Pamela J. Bjorkman, Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125. Tel:626-395-8350 Fax:626-792-3683 E-mail:bjorkman{at}cco.caltech.edu.
The macrophage and epithelial cell mannose receptor (MR) binds carbohydrates on foreign and host molecules. Two portions of MR recognize carbohydrates: tandemly arranged C-type lectin domains facilitate carbohydrate-dependent macrophage uptake of infectious organisms, and the NH2-terminal cysteine-rich domain (Cys-MR) binds to sulfated glycoproteins including pituitary hormones. To elucidate the mechanism of sulfated carbohydrate recognition, we determined crystal structures of Cys-MR alone and complexed with 4-sulfated-N-acetylgalactosamine at 1.7 and 2.2 Å resolution, respectively. Cys-MR folds into an approximately three-fold symmetric ß-trefoil shape resembling fibroblast growth factor. The sulfate portions of 4-sulfated-N-acetylgalactosamine and an unidentified ligand found in the native crystals bind in a neutral pocket in the third lobe. We use the structures to rationalize the carbohydrate binding specificities of Cys-MR and compare the recognition properties of Cys-MR with other ß-trefoil proteins.
Key Words: ß-trefoil protein, hydrogen bond network, multilectin receptor, pituitary hormones, sulfated GalNAc
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