The glycosylation of human serum IgD and IgE and the accessibility of identified oligomannose structures for interaction with mannan-binding lectin

Arnold, James N., Radcliffe, Catherine M., Wormald, Mark R., Royle, Louise, Harvey, David J., Crispin, Max, Dwek, Raymond A., Sim, Robert B. and Rudd, Pauline M. (2004) The glycosylation of human serum IgD and IgE and the accessibility of identified oligomannose structures for interaction with mannan-binding lectin. Journal of Immunology, 173 (11), 6831-6840.

Abstract

Analysis of the glycosylation of human serum IgD and IgE indicated that oligomannose structures are present on both Igs. The relative proportion of the oligomannose glycans is consistent with the occupation of one N-linked site on each heavy chain. We evaluated the accessibility of the oligomannose glycans on serum IgD and IgE to mannan-binding lectin (MBL). MBL is a member of the collectin family of proteins, which binds to oligomannose sugars. It has already been established that MBL binds to other members of the Ig family, such as agalactosylated glycoforms of IgG and polymeric IgA. Despite the presence of potential ligands, MBL does not bind to immobilized IgD and IgE. Molecular modeling of glycosylated human IgD Fc suggests that the oligomannose glycans located at Asn³⁵⁴ are inaccessible because the complex glycans at Asn⁴⁴⁵ block access to the site. On IgE, the additional C _H2 hinge domain blocks access to the oligomannose glycans at Asn ³⁹⁴ on one H chain by adopting an asymmetrically bent conformation. IgE contains 8.3% Man₅GlcNAc₂ glycans, which are the trimmed products of the Glc₃Man₉GlcNAc₂ oligomannose precursor. The presence of these structures suggests that the C_H2 domain flips between two bent quaternary conformations so that the oligomannose glycans on each chain become accessible for limited trimming to Man₅GlcNAc₂ during glycan biosynthesis. This is the first study of the glycosylation of human serum IgD and IgE from nonmyeloma proteins.

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Contributors

Author: Max Crispin

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