Uncovering Nonconventional and Conventional Hydrogen Bonds in Oligosaccharides through NMR Experiments and Molecular Modeling: Application to Sialyl Lewis-X

Abstract

We describe the direct NMR detection of a C-H···O nonconventional hydrogen bond (Hbond) and provide experimental and theoretical evidence for conventional Hbonds in the pentasaccharide sialyl Lewis-X (sLe(X)-5) between 5 and 37 °C in water. Extensive NMR structural studies together with molecular dynamics simulations offer strong evidence for significant local dynamics in the Le(X) core and for previously undetected conventional Hbonds in rapid equilibrium that modulate structure. These NMR studies also showed temperature-dependent (1)H and (13)C line broadening. The resulting model emerging from this study is more complex than a simple rigid core description of Le(X)-like molecules and improves our understanding of stabilizing interactions in glycans.

Structural basis for sulfation-dependent self-glycan recognition by the human immune-inhibitory receptor Siglec-8

“…4F), as has been found previously in structures of Le x (37) and sLe x (38) oligosaccharides. The presence of this hydrogen bond is indicated by the distance between Fuc-H5 and Gal-O5 of 2.2-2.3 Å within the ensemble, which is significantly shorter than the sum of the corresponding van der Waals radii (2.6 Å), and further supported by the characteristic NMR chemical shift of Fuc-H5 (∼4.8 ppm) (37,38).…”

“…However, Fuc stabilizes the core Le x trisaccharide in a binding-competent conformation by forming an intracarbohydrate C-H···O hydrogen bond to Gal6S (Fig. 4F), together with hydrophobic interactions (37,38,43), and may thus indirectly contribute to affinity by decreasing the entropic penalty of fixing multiple conformational degrees of freedom upon binding.…”

Minimizing the Entropy Penalty for Ligand Binding: Lessons from the Molecular Recognition of the Histo Blood‐Group Antigens by Human Galectin‐3

“…[12,21] Our NMR and MD results (see the Supporting Information for details) agree with the existence of as ingle conformational family for 2, 4 and 5.The situation is rather different for the non-fucosylated trisaccharide 3,f or which MD simulations predict that the Gala1-3Galb linkage is rather flexible, with continuous transitions along the entire trajectory between the syn-F/syn(À)-Y and syn-F/syn(+ +)-Y geometries ( Figure 5B). [12,21] Our NMR and MD results (see the Supporting Information for details) agree with the existence of as ingle conformational family for 2, 4 and 5.The situation is rather different for the non-fucosylated trisaccharide 3,f or which MD simulations predict that the Gala1-3Galb linkage is rather flexible, with continuous transitions along the entire trajectory between the syn-F/syn(À)-Y and syn-F/syn(+ +)-Y geometries ( Figure 5B).…”

“…This lectin has been related to several diseases,and it is actually atarget for the development of high-affinity ligands as antagonists for the treatment of certain cancers and fibrotic diseases. [12] Thep reorganization of the ligand in the bound geometry eliminates the conformational selection event for complex formation, lowers the energy barrier for the association, increases the on-rate and impacts the binding entropy.A saconsequence,t he fucosylated tetrasaccharides bind more strongly than their trisac-charide parent analogues,thus making BGA/hGal-3 an ideal system to unmask the commonly hidden contribution of ligand conformational entropy in binding events. [11] However,the basis for this stronger interaction has not been clarified.…”

Minimizing the Entropy Penalty for Ligand Binding: Lessons from the Molecular Recognition of the Histo Blood‐Group Antigens by Human Galectin‐3

“…Interestingly,t he presence of the Fuc moiety has been previously shown to restrict the conformational mobility of branched oligosaccharides, including BGA and Le x antigens. [12] Thep reorganization of the ligand in the bound geometry eliminates the conformational selection event for complex formation, lowers the energy barrier for the association, increases the on-rate and impacts the binding entropy.A saconsequence,t he fucosylated tetrasaccharides bind more strongly than their trisac-charide parent analogues,thus making BGA/hGal-3 an ideal system to unmask the commonly hidden contribution of ligand conformational entropy in binding events.…”