Structural characterization of the DC-SIGN-Lewis(X) complex.

Area of Science:

• * Molecular and Structural Biology
• * Immunology
• * Glycobiology

Background:

• * Dendritic cell-specific intracellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) is a C-type lectin on dendritic cells.
• * DC-SIGN mediates cell-cell and pathogen interactions by binding mannose or fucose residues.
• * Understanding DC-SIGN binding is crucial for developing therapeutics for immune-related diseases.

Purpose of the Study:

• * To structurally characterize the interaction between the DC-SIGN carbohydrate recognition domain (CRD) and Lewis X (Le(X)).
• * To elucidate the binding epitopes and conformations of Le(X) when bound to DC-SIGN.
• * To generate and validate structural models of the DC-SIGN CRD-Le(X) complex.

Main Methods:

• * Nuclear Magnetic Resonance (NMR) spectroscopy, including 2D NMR, (1)H-(15)N HSQC, saturation transfer difference (STD), and transferred nuclear Overhauser effect (trNOE).
• * NMR titration experiments with monomeric and tetrameric forms of DC-SIGN CRD and Le(X).
• * Computational modeling using NMR-derived restraints to generate binding models.

Main Results:

• * NMR titrations identified key residues in the DC-SIGN CRD binding site for Le(X).
• * STD and trNOE experiments revealed specific binding epitopes and the bound conformation of Le(X).
• * Generated structural models suggested Le(X) binding conformations distinct from previously reported crystal structures.

Conclusions:

• * Novel structural insights into the binding of Lewis X to DC-SIGN CRD were obtained.
• * The identified conformations provide a basis for understanding differential binding of various saccharides by DC-SIGN.
• * These findings can inform the design of mimetics to modulate DC-SIGN-mediated immune responses.