Evidence for two populated conformations for the dimeric LeX and LeALeX tumor associated carbohydrate antigens.
The conformational behavior of tumor associated carbohydrate antigens (TACAs) dimLex and LeaLex was studied using a combination of NMR experiments and molecular dynamic simulations. It is shown that within the hexasaccharides, the Lex and Lea branched trisaccharides fragments adopt the rigid “stacked” conformation known for the isolated trisaccharide antigens. In contrast, the β-D-GlcNAc-(1→3)-D-Gal glycosidic bond that connects the two Lex trisaccharides in dimLex, and the Lea trisaccharide to the Lex trisaccharide in LeaLex was found to be very flexible in both hexasaccharides. Our results show that two distinct conformations differing by the value of the Ψ angle for this glycosidic bond, are populated in solution. While the relative proportions of the two conformations in solution could not be determined accurately, experimental measurements indicate that both conformations are populated in significant amounts.