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Published January 19, 2001 | public
Journal Article

The molecular mechanism of sulfated carbohydrate recognition by the cysteine-rich domain of mannose receptor

Abstract

The mannose receptor (MR) binds foreign and host ligands through interactions with their carbohydrates. Two portions of MR have distinct carbohydrate recognition properties. One is conferred by the amino-terminal cysteine-rich domain (Cys-MR), which plays a critical role in binding sulfated glycoproteins including pituitary hormones. The other is achieved by tandemly arranged C-type lectin domains that facilitate carbohydrate-dependent uptake of infectious microorganisms. This dual carbohydrate binding specificity enables MR to bind ligands by interacting with both sulfated and non-sulfated polysaccharide chains. We previously determined crystal structures of Cys-MR complexed with 4-SO_4-N-acetylglucosamine and with an unidentified ligand resembling Hepes (N-[2-hydroxyethyl]piperazine-N′-[2-ethanesulfonic acid]). In continued efforts to elucidate the mechanism of sulfated carbohydrate recognition by Cys-MR, we characterized the binding affinities between Cys-MR and potential carbohydrate ligands using a fluorescence-based assay. We find that Cys-MR binds sulfated carbohydrates with relatively high affinities (K_D=0.1 mM to 1.0 mM) compared to the affinities of other lectins. Cys-MR also binds Hepes with a K_D value of 3.9 mM, consistent with the suggestion that the ligand in the original Cys-MR crystal structure is Hepes. We also determined crystal structures of Cys-MR complexed with 3-SO_4-Lewis^x, 3-SO_4-Lewis^a, and 6-SO_4-N-acetylglucosamine at 1.9 Å, 2.2 Å, and 2.5 Å resolution, respectively, and the 2.0 Å structure of Cys-MR that had been treated to remove Hepes. The conformation of the Cys-MR binding site is virtually identical in all Cys-MR crystal structures, suggesting that Cys-MR does not undergo conformational changes upon ligand binding. The structures are used to rationalize the binding affinities derived from the biochemical studies and to elucidate the molecular mechanism of sulfated carbohydrate recognition by Cys-MR.

Additional Information

© 2001 Academic Press. Received 20 August 2000, Revised 1 November 2000, Accepted 6 November 2000. We thank Ten Feizi, Christine Leteux, Heide Kogelberg, and members of the Bjorkman laboratory for critical reading of the manuscript, and Michel Nussenzweig for contributions to earlier phases of the project. Data bank accession numbers: Coordinates have been deposited in the RCSB Protein Data Bank under accession codes 1FWV (3-SO4-Lewisa complex) and 1FWU (3-SO4-Lewisx complex).

Additional details

Created:
August 21, 2023
Modified:
October 25, 2023