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 13 C-enriched Neu5Acα2−3Galβ1−4(Fucα1−3)GlcNAc (sialyl Lewis x ), together with its bound-state conformation in association with E-selectin. The availability of 13 C-enriched material enabled both the measurement of trans-glycosidic 13 C− 13 C coupling constants as conformational probes in the tetrasaccharide and the application of three-dimensional nuclear Overhauser effect 13 C− 1 H 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 ( 13 C) 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.