Stable-isotope-assisted NMR studies on 13C-enriched sialyl Lewisx in solution and bound to E-selectin

We report the determination of the solution structure and dynamics of C-13-enriched Neu5Ac alpha 2-3Gal beta 1 -4(Fuc alpha 1-3)GlcNAc (sialyl Lewis(x)), together with its bound-state conformation in association with E-selectin. The availability of C-13-enriched material enabled both the measurement of trans-glycosidic C-13-C-13 coupling constants as conformational probes in the tetrasaccharide and the application of three-dimensional nuclear Overhauser effect C-13-H-1 heteronuclear single-quantum correlation experiments for the measurement of intramolecular transferred nuclear Overhauser effects (TRNOEs) characterizing the bound-state conformation of the ligand. The additional dispersion afforded by the third (C-13) dimension permitted straightforward identification and quantitation of these TRNOEs, and several TRNOEs were identified that had not previously been reported. The bound-state conformation of the ligand, determined by use of a heteronuclear full-relaxation matrix analysis of the TRNOE data, differs significantly from that reported in previous studies.