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Aberrant glycosylation occurs in the majority of human cancers and changes in mucin-type O-glycosylation are key events that play a role in the induction of invasion and metastases. These changes generate novel cancer-specific glyco-antigens that can interact with cells of the immune system through carbohydrate binding lectins. Two glyco-epitopes that are found expressed by many carcinomas are Tn (GalNAc-Ser/Thr) and STn (NeuAcα2,6GalNAc-Ser/Thr). These glycans can be carried on many mucin-type glycoproteins including MUC1. We show that the majority of breast cancers carry Tn within the same cell and in close proximity to extended glycan T (Galβ1,3GalNAc) the addition of Gal to the GalNAc being catalysed by the T synthase. The presence of active T synthase suggests that loss of the private chaperone for T synthase, COSMC, does not explain the expression of Tn and STn in breast cancer cells. We show that MUC1 carrying both Tn or STn can bind to the C-type lectin MGL and using atomic force microscopy show that they bind to MGL with a similar deadadhesion force. Tumour associated STn is associated with poor prognosis and resistance to chemotherapy in breast carcinomas, inhibition of DC maturation, DC apoptosis and inhibition of NK activity. As engagement of MGL in the absence of TLR triggering may lead to anergy, the binding of MUC1-STn to MGL may be in part responsible for some of the characteristics of STn expressing tumours.

The morphologies of the compacted semiflexible biological polyanions alginate, acetan, circular plasmid DNA, and xanthan were investigated using tapping mode atomic force microscopy followed by quantitative image analysis. A shape factor was calculated for each of the observed polyelectrolyte complexes and used as a basis for dividing the structures into ensembles of morphologically linear, toroidal, and globular structures for subsequent quantitative analysis. Compaction of polyanions with chitosan yielded a small fraction of the torus morphology when the persistence length, L p, of 25 nm (acetan) was reached. For both DNA, L p = 50 nm, and xanthan, L p = 120 nm, it was found that the toroids make up a substantial fraction of the complexed structures formed by the given chitosan and at room temperature. Rodlike complexes were additionally observed within DNA−chitosan complexes, whereas they do not appear as a significant fraction of chitosan-complexed high-molecular-weight xanthan. The average height of the condensates was observed to be ∼2 nm for the compacted xanthan toroids, while it was determined to be ∼5 nm for compacted DNA toroids. Reducing the degree of polymerization of xanthan yielded a decrease in the fraction of toroids. Compacted xanthan at room temperature displays a number of racquets and other morphologies similar to the reported intermediate, metastable states by simulations. The reduced abundance of such structures following annealing supports the interpretation of their metastable nature.

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The compaction of the semiflexible polysaccharide xanthan with selected multi- and polyvalent cations was studied. Polyelectrolyte complexes prepared at concentrations of 1-2 microg/ml were observed by tapping mode atomic force microscopy. High-molecular-weight xanthan compacted with chitosan yields a blend of mainly toroidal and metastable structures and a small fraction of rod-like species. Polyelectrolyte complexes of xanthan with polyethylenimine and trivalent chromium yielded similar structures or alternatively less well packed species. Racquet-type morphologies were identified as kinetically trapped states occurring on the folding path toward the energetically stable state of the toroids. Thermal annealing yielded a shift of the distribution of xanthan-chitosan morphologies toward this stable state. Ensembles of toroidal and rod-like morphologies of the xanthan-chitosan structures, collected using an asphericity index, were analyzed. The mean height of the toroids increased upon heating, with a selective increase in the height range above 2 nm. It is suggested that the observed metastable structures are formed from the high-molecular-weight fraction of xanthan and that these are driven toward the toroidal state, being a low-energy state, following annealing. Considered a model system for condensation of semiflexible polymers, the compaction of xanthan by chitosan captures the system at various stages in the folding toward a low-energy state and thus allows experimental analyses of these intermediates and their evolution.