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

Abstract

Ligand conformational entropy plays an important role in carbohydrate recognition events. Glycans are characterized by intrinsic flexibility around the glycosidic linkages, thus in most cases, loss of conformational entropy of the sugar upon complex formation strongly affects the entropy of the binding process. By employing a multidisciplinary approach combining structural, conformational, binding energy, and kinetic information, we investigated the role of conformational entropy in the recognition of the histo blood‐group antigens A and B by human galectin‐3, a lectin of biomedical interest. We show that these rigid natural antigens are pre‐organized ligands for hGal‐3, and that restriction of the conformational flexibility by the branched fucose (Fuc) residue modulates the thermodynamics and kinetics of the binding process. These results highlight the importance of glycan flexibility and provide inspiration for the design of high‐affinity ligands as antagonists for lectins.

Binding of Gold(III) Porphyrin by the Pro-metastatic Regulatory Protein Human Galectin-3

“…The measurements of binding constants obtained using MST, TFS and ITC and even molecular docking are consistent with the Au 3+ TPPS-Gal3 FL interaction of low micromolar affinity. The affinity of Au 3+ TPPS for Gal3 FL is higher than for LacNAc with one binding site but lower than for asialofetuin (K D = 720 nM) with nine LacNAc epitopes [57] and is the same as for blood group type II [45]. Similar to the interaction with oligosaccharides and the asialofetuin glycoprotein, the binding of Au 3+ TPPS is enthalpically driven, however the entropic contribution to binding is also positive.…”

“…However, H(2)TPPS binds by intruding, overlapping or allosterically hindering the carbohydrate-binding sites of concanavalin A, peanut agglutininin and jacalin, respectively, therefore porphyrin binding might negatively interfere with the highly selective cancer-antigen targeting function of the plant lectins [38]. An earlier study demonstrated that zinc tetrasulfonatophenylporphyrin (Zn 2+ TTPS) binds Gal3 with high affinity (K d = 0.18 µM) [42], largely surpassing N-acetyllactosamine, that is generally considered to be a specific binder of Gal3, with reported affinities K d = 25 µM [43], 28 µM [44], 112 µM [45] and 118 µM [46]. Most importantly, lactose did not inhibit Zn 2+ TTPS binding [42], suggesting that carbohydrate binding might be compatible with the binding of the porphyrin photosensitizers.…”

Regioselective Glycosylation Strategies for the Synthesis of Group Ia and Ib Streptococcus Related Glycans Enable Elucidating Unique Conformations of the Capsular Polysaccharides

“…However,g iven their intrinsic flexibility,e specially for Ib, both molecules could be accommodated to interactw ith the monoclonal binding pockets without am ajor entropyp enalty. [31]…”

Increasing the Affinity of an O‐Antigen Polysaccharide Binding Site in Shigella flexneri Bacteriophage Sf6 Tailspike Protein

“…However, no common strategy exists for a rational selection of mutations for design of high‐affinity carbohydrate‐binding proteins. The inherent flexibility of the glycan ligand often has major impact on the energetics of protein–carbohydrate complex formation . Flexibility in glycans can be functional to sample a large conformational space for binding sites and provide higher avidity in multivalent settings .…”