Molecular Insights into DC-SIGN Binding to Self-Antigens: The Interaction with the Blood Group A/B Antigens

Abstract

The dendritic cell-specific intracellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) is an important receptor of the immune system. Besides its role as pathogen recognition receptor (PRR), it also interacts with endogenous glycoproteins through the specific recognition of self-glycan epitopes, like Le X . However, this lectin represents a paradigmatic case of glycan binding promiscuity, and it also has been shown to recognize antigens with α1−α2 linked fucose, such as the histo blood group antigens, with similar affinities to Le X . Herein, we have studied the interaction in solution between DC-SIGN and the blood group A and B antigens, to get insights into the atomic details of such interaction. With a combination of different NMR experiments, we demonstrate that the Fuc coordinates the primary Ca 2+ ion with a single binding mode through 3-OH and 4-OH. The terminal αGal/αGalNAc affords marginal direct polar contacts with the protein, but provides a hydrophobic hook in which V351 of the lectin perfectly fits. Moreover, we have found that αGal, but not αGalNAc, is a weak binder itself for DC-SIGN, which could endow an additional binding mode for the blood group B antigen, but not for blood group A.

Three-Dimensional Structures of Carbohydrates and Where to Find Them

“…Advances in NMR methods hold great potential for direct spatial structure determination of carbohydrate-protein complexes in solution based on intermolecular NOEs which affords estimation of atomic contacts between a protein and a carbohydrate ligand [ 97 , 98 ]. Further extraction of NOE-derived distance restraints for a saccharide molecule results in generation of representative conformational ensembles [ 99 , 100 , 101 ].…”

“…Vast variety of methods provide information about 3D structure of individual glycans and glycan moieties of glycoproteins and protein-carbohydrate complexes ( Figure 6 ) [ 285 , 286 ]. The following approaches are most utilized for 3D structural data validation [ 287 , 288 , 289 ]: Ccombination of carbohydrate simulated geometry data with X-ray crystallographic data analysis [ 225 , 290 ]; Analysis of inter-glycosidic NMR spin couplings, which depend on glycosidic bond torsions [ 114 , 291 , 292 ]; Deriving nuclear Overhauser effects (NOEs) from relative populations of the interatomic distances, with subsequent comparison to the experimental NOEs in solution [ 99 , 293 , 294 ]; Purely informatic detection of errors, such as incompatible atomic coordinates originating from incorrect processing or simulation [ 295 , 296 , 297 , 298 ]; Simulation by other computational methods at higher levels of theory [ 102 , 103 , 105 , 108 ]. …”

“…Deriving nuclear Overhauser effects (NOEs) from relative populations of the interatomic distances, with subsequent comparison to the experimental NOEs in solution [ 99 , 293 , 294 ];…”

“…NMR techniques are a powerful approach to investigate conformational and dynamic behavior of carbohydrate moieties in biomolecules [ 307 , 308 , 309 , 310 ]. However, the nature of NOE enhancement factor has been hampering obtaining the sufficient number of distance restrains [ 99 ]. In the case of saccharides with their multiple rotatable bonds, the stable 3D structure was difficult to define, making molecular modeling essential for this class of compounds.…”

A Peptide–Lectin Fusion Strategy for Developing a Glycan Probe for Use in Various Assay Formats

“…Extracellular human C-type lectins, such as DC-SIGN (dendritic cell specific intercellular adhesion molecule-3 grabbing non-integrin) and MBL (mannose binding lectin), can bind aberrant oligomannosylation, requiring a calcium ion for coordination with the glycan, to facilitate their removal [28]. It has been reported that monosaccharide fucose units can also coordinate with the calcium ion in DC-SIGN and even manifest interaction with α1−α2 linked fucose as presented by histo blood group antigens, highlighting a prime example of the cross-specificity or promiscuity that exists in many lectins [29,30]. There are also several plant and microbe derived lectins that recognize oligomannose units in a calcium independent manner including Pseudomonas fluorescens agglutinin (PFA), which is a member of the Oscillatoria agardhii agglutinin homologue family of lectins capable of recognizing the Man alpha(1-3)-Man alpha(1-6)-Man core [31] present on high mannose and hybrid type glycans.…”