Application of homonuclear 3D NMR experiments and 1D analogs to study the conformation of sialyl Lewisx bound to E-selectin

The conformation of the sialyl Lewis ^x tetrasaccharidebound to E-selectin was previously determined from transfer NOE (trNOE)experiments in conjunction with a distance-geometry analysis. However, theorientation of the tetrasaccharide ligand in the binding site of E-selectinis still unknown. It can be predicted that the accurate quantitativeanalysis of all trNOEs, including those originating from spin diffusion, isone key to analyze the orientation of sialyl Lewis^x in thebinding pocket of E-selectin. Therefore, we applied homonuclear 3D NMRexperiments and 1D analogs to obtain trNOEs that could not unambiguously beassigned from previous 2D trNOESY spectra, due to severe resonance-signaloverlap. A 3D TOCSY-trNOESY experiment, a 1D TOCSY-trNOESY experiment, and a1D trNOESY-TOCSY experiment of the sialyl Lewis^x/E-selectincomplex furnished new interglycosidic trNOEs and provided additionalinformation for the interpretation of trNOEs that have been describedbefore. A 2D trROESY spectrum of the sialyl Lewis^x/E-selectincomplex allowed one to identify the amount of spin-diffusion contributionsto trNOEs. Finally, an unambiguous assignment of all trNOEs, and an analysisof spin-diffusion pathways, was obtained, creating a basis for aquantitative analysis of trNOEs in the sialylLewis^x/E-selectin complex.