The intrinsic conformation of a Lewis antigen: The Lewis × trisaccharide

The conformation of the Lewisx antigen has been determined, free of environmental perturbation, at low temperature in the gas phase to reveal a global minimum energy structure lying below the rigid stacked conformations adopted in aqueous solution, in the crystalline hydrate or when bound to proteins. The result suggests that water plays a key structural role in controlling the conformation of Lewisx and in consequence, its biological function.