Lewis X trisaccharides normally function as essential cell-cell interaction mediators. However, oligomers of Lewis X trisaccharides expressed by the parasite Schistosoma mansoni seem to be related to its evasion of the immune response of its human host. Here we show that monoclonal antibody 54-5C10-A, which is used to diagnose schistosomiasis in humans, interacts with oligomers of at least three Lewis X trisaccharides, but not with monomeric Lewis X. We describe the sequence and the 2.5 A crystal structure of its Fab fragment and infer a possible mode of binding of the polymeric Lewis X from docking studies. Our studies indicate a radically different mode of binding compared to Fab 291-2G3-A, which is specific for monomeric Lewis X, thus providing a structural explanation of the diagnostic success of 54-5C10-A.
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Article Synopsis
- Protonated fucose-containing oligosaccharides often rearrange during mass spectrometry, creating complex fragments that complicate analysis.
- This study utilizes density functional theory to analyze IR spectra of specific trisaccharides, concluding that they do not undergo rearrangement in the gas phase.
- Key factors for rearrangement include the presence of a mobile proton and the stability differences between the parent ions and their rearranged forms.
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