Structural Basis for Distinct Binding Properties of the Human Galectins to Thomsen-Friedenreich Antigen

Abstract

The Thomsen-Friedenreich (TF or T) antigen, Galβ1-3GalNAcα1-O-Ser/Thr, is the core 1 structure of O-linked mucin type glycans appearing in tumor-associated glycosylation. The TF antigen occurs in about 90% of human cancer cells and is a potential ligand for the human endogenous galectins. It has been reported that human galectin-1 (Gal-1) and galectin-3 (Gal-3) can perform their cancer-related functions via specifically recognizing TF antigen. However, the detailed binding properties have not been clarified and structurally characterized. In this work, first we identified the distinct TF-binding abilities of Gal-1 and Gal-3. The affinity to TF antigen for Gal-3 is two orders of magnitude higher than that for Gal-1. The structures of Gal-3 carbohydrate recognition domain (CRD) complexed with TF antigen and derivatives, TFN and GM1, were then determined. These structures show a unique Glu-water-Arg-water motif-based mode as previously observed in the mushroom galectin AAL. The observation demonstrates that this recognition mode is commonly adopted by TF-binding galectins, either as endogenous or exogenous ones. The detailed structural comparisons between Gal-1 and Gal-3 CRD and mutagenesis experiments reveal that a pentad residue motif (51AHGDA55) at the loop (g1-L4) connecting β-strands 4 and 5 of Gal-1 produces a serious steric hindrance for TF binding. This motif is the main structural basis for Gal-1 with the low affinity to TF antigen. These findings provide the intrinsic structural elements for regulating the TF-binding activity of Gal-1 in some special conditions and also show certain target and approach for mediating some tumor-related bioactivities of human galectins.

Synthesis and cell-selective antitumor properties of amino acid conjugated tumor-associated carbohydrate antigen-coated gold nanoparticles

“…Recent structural work on Gal-3/TF ag complexes has shown that in vitro dissociation constants for this carbohydrate-protein interaction are ~47 uM for monomeric TF-Threonine. 88 If a “direct” relationship exists between binding Gal-3 and cytotoxicity in SU-DHL-6 cells, coating AuNPs with TF ag -Thr would have increased potency by about one order of magnitude compared to the dissociation constant concentration. While not conclusive and requiring further testing, the cellular toxicity data described here suggests a selective interaction of the particles with Gal-3.…”

Stromal galectin-1 expression is associated with long-term survival in resectable pancreatic ductal adenocarcinoma

“…A recent study suggested that galectin-1 could directly interact with the Thomsen-Friedenreich (TF or T) antigen (Galβ1-3GalNAcα1-O-Ser/Thr), which is the core 1 structure of O-linked mucin type glycans appearing in tumorassociated glycosylation. 34 It would be interesting to further investigate whether and how the interactions of galectin-1 and mucins confer functional significance in promoting tumor progression and invasion in pancreatic cancer.…”

Binding of Galectin-3, a β-Galactoside-binding Lectin, to MUC1 Protein Enhances Phosphorylation of Extracellular Signal-regulated Kinase 1/2 (ERK1/2) and Akt, Promoting Tumor Cell Malignancy

“…In this context, it has been reported that although the galectin family exhibits high affinity for ␤-galactoside-containing carbohydrate moieties such as TF antigen, its affinity for each ␤-galactoside-containing carbohydrate moiety differs among galectins (40,41). In the case of TF antigen, galectin-3 exhibits a higher affinity than galectin-1 does (41,42). Therefore, although both galectin-1 and -3 may be secreted extracellularly, as shown in Fig.…”