Paradigms for glycan-binding receptors in cell adhesion

Diverse glycans found on the surfaces of mammalian cells provide a basis for selective adhesion between cells mediated by glycan-specific receptors. Well-understood examples of cell adhesion based on such interactions include selectin-mediated rolling of leukocytes on endothelia. Other receptors with similar selectivity for specific sugar epitopes on cell surfaces are being characterised. However, the simple paradigm of adhesion resulting from receptors on one cell binding to glycans on another cell applies in only a limited number of systems. Instead, glycans and receptor-glycan interactions often modulate adhesion in indirect ways, such as by changing the organisation of cell surface glycoproteins and by antagonising the effect of protein adhesion systems.