Interactions of mucins with the Tn or Sialyl Tn cancer antigens including MUC1 are due to GalNAc–GalNAc interactions

Abstract

The molecular mechanism(s) underlying the enhanced self-interactions of mucins possessing the Tn (GalNAcα1-Ser/Thr) or STn (NeuNAcα2-6GalNAcα1-Ser/Thr) cancer markers were investigated using optical tweezers (OT). The mucins examined included modified porcine submaxillary mucin containing the Tn epitope (Tn-PSM), ovine submaxillary mucin with the STn epitope (STn-OSM), and recombinant MUC1 analogs with either the Tn and STn epitope. OT experiments in which the mucins were immobilized onto polystyrene beads revealed identical self-interaction characteristics for all mucins. Identical binding strength and energy landscape characteristics were also observed for synthetic polymers displaying multiple GalNAc decorations. Polystyrene beads without immobilized mucins showed no self-interactions and also no interactions with mucin-decorated polystyrene beads. Taken together, the experimental data suggest that in these molecules, the GalNAc residue mediates interactions independent of the anchoring polymer backbone. Furthermore, GalNAc-GalNAc interactions appear to be responsible for self-interactions of mucins decorated with the STn epitope. Hence, Tn-MUC1 and STn-MUC1 undergo self-interactions mediated by the GalNAc residue in both epitopes, suggesting a possible molecular role in cancer. MUC1 possessing the T (Galβ1-3GalNAcα1-Ser/Thr) or ST antigen (NeuNAcα2-3Galβ1-3GalNAcα1-Ser/Thr) failed to show self-interactions. However, in the case of ST-MUC1, self-interactions were observed after subsequent treatment with neuraminidase and β-galactosidase. This enzymatic treatment is expected to introduce Tn-epitopes and these observations thus further strengthen the conclusion that the observed interactions are mediated by the GalNAc groups.

The Role of Glycans in Bacterial Adhesion to Mucosal Surfaces: How Can Single-Molecule Techniques Advance Our Understanding?

“…Cohen and Varki argue that “ it is likely that glycan microdomains are mostly stabilized by carbohydrate–carbohydrate interactions, which are too weak to withstand the standard biochemical methods used to study protein–protein interactions (e.g., immunoprecipitation). ” The later evidence for the ability of mucins of varying glycosylation pattern to form interactions, as provided using both AFM [ 152 , 153 ] and OT [ 154 ], strengthens this hypothesis.…”

“…To date, only one example shows the utility of this technique to measure glycan-glycan interactions. In 2016, Haugstad et al showed that OT could be used to measure the adhesion forces between self-associating mucins presenting particular glycan structures [ 154 ]. The experimental data provided in the paper ( Figure 4 b) allowed the authors to conclude that a particular glycan structure, the N -acetylgalactosamine (GalNAc), was responsible for the self-interactions observed for the mucins.…”

“…( b ) OT schematic representation and force curves obtained when probing the self-interactions between two polystyrene beads functionalized with mucins MUC1 harboring different glycan decorations (Tn-MUC1, STn-MUC1 and ST-MUC1). Reprinted with permissions from [ 154 ].…”

Tumor‐associated antigens: Tn antigen, sTn antigen, and T antigen

“…However, sTn antigen may promote tumor cells to migrate and invade underlying tissue, and eventually reach blood or lymph vessels . All the evidences mentioned above suggest that sTn antigen plays a transient role in the progression of cancer .…”

Glycan–glycan interactions determine Leishmania attachment to the midgut of permissive sand fly vectors

“…To put this mode of binding in context, and accepting that there will be variations between experimental conditions, the average binding affinity of L. mexicana nectomonad LPG for GalNAc is comparable to other protein-glycan interactions between bacterial pili and mucins; 43,44 bacterial pili and host pneumocytes; 45 bacterial adhesins; [46][47][48] and soybean agglutinin and porcine gastric mucin, 49 and greater than a range of glycan-glycan interactions recorded within selfassembling mucins. [50][51][52] Sample force curves showing extension and rupture of single and multiple bonds between functionalized AFM tips and a strongly adhesive WT L. mexicana nectomonad promastigote are shown in Fig. 4c and d, respectively.…”