Solution structure of two xenoantigens:: αGal-LacNAc and αGal-Lewis X

Organ hyperacute rejection, a phenomenon occurring during discordant xenotransplantation, is due to the recognition of an oligosaccharide epitope by human xenoreactive natural antibodies. In addition to the alphaGal(1-3)betaGal(1-4)GlcNAc trisaccharide, a fucosylated structure, alphaGal-Lewis X, has been shown to be recognized by the antibodies. Both the trisaccharide and the tetrasaccharide have been synthesized by chemical methods. A complete nuclear magnetic resonance characterization of the two compounds has been performed, including the measurements of two-dimensional nuclear Overhauser effect spectroscopy data. Molecular dynamics simulations were run for several ns in the presence of explicit water molecules. The combination of experimental and theoretical approaches revealed the effect of an additional fucose residue on the conformational behavior of the xenoantigen. This branched fucose strongly rigidifies the N-acetyllactosamine. The effect on the alphaGal(1-3)Gal fragment is less marked. In the presence of fucose, the terminal alphaGal residue can still adopt two different conformations, but the equilibrium populations are modified.