Human galectin-3 (Mac-2 antigen): Defining molecular switches of affinity to natural glycoproteins, structural and dynamic aspects of glycan binding by flexible ligand docking and putative regulatory sequences in the proximal promoter region

BackgroundHuman galectin-3 (Mac-2 antigen) is a cell-type-specific multifunctional effector owing to selective binding of distinct cell-surface glycoconjugates harboring β-galactosides. The structural basis underlying the apparent preferences for distinct glycoproteins and for expression is so far unknown.MethodsWe strategically combined solid-phase assays on 43 natural glycoproteins with a new statistical approach to fully flexible computational docking and also processed the proximal promoter region in silico.ResultsThe degree of branching in N-glycans and clustering of core 1 O-glycans are positive modulators for avidity. Sialylation of N-glycans in α2–6 linkage and of core 1 O-glycans in α2–3 linkage along with core 2 branching was an unfavorable factor, despite the presence of suited glycans in the vicinity. The lectin–ligand contact profile was scrutinized for six natural di- and tetrasaccharides enabling a statistical grading by analyzing flexible docking trajectories. The computational analysis of the proximal promoter region delineated putative sites for Lmo2/c-Ets-1 binding and new sites with potential for RUNX binding.General significanceThese results identify new features of glycan selectivity and ligand contact by combining solid-phase assays with in silico work as well as of reactivity potential of the promoter.

Graphical AbstractProtein–carbohydrate recognition is involved in diverse medical processes. Using an adhesion/growth-regulatory human lectin as model, ligand contact is computationally processed by flexible ligand docking. Binding assays with glycoproteins take analysis of selectivity to the level of natural ligands delineating relevance of branching.Figure optionsDownload high-quality image (63 K)Download as PowerPoint slideResearch Highlights
► Degree of N-glycan branching/core 1 O-glycan clustering enhances galectin-3 binding.
► Core 2 O-glycan branching, core 1 O-glycan α2,3-sialylation and N-glycan α2,6-sialylation reduce affinity.
► Flexible ligand docking with a statistical approach quantitates transient contacts.
► Computational promoter analysis identifies new sites with potential to explain the cell-type-specific profile.