Establishing Rules for Self-Adhesion and Aggregation of -Glycan Sugars Using Virus Glycan Shields.

The surfaces of cells and pathogens are covered with short polymers of sugars known as glycans. Complex -glycans have a core of three mannose sugars with distal repeats of -acetylglucosamine and galactose sugars terminating with sialic acid (SA). Long-range tough and short-range brittle self-adhesions were observed between SA and mannose residues, respectively, in ill-defined artificial monolayers. We investigated if and how these adhesions translate when the residues are presented in -glycan architecture with SA at the surface and mannose at the core and with other glycan sugars. Two pseudotyped viruses with complex -glycan shields were brought together in force spectroscopy (FS). At higher ramp rates, slime-like adhesions were observed between the shields, whereas Velcro-like adhesions were observed at lower rates. The higher approach rates compress the virus as a whole, and the self-adhesion between the surface SA is sampled. At the lower ramp rates, however, the complex glycan shield is penetrated and adhesion from the mannose core is accessed. The slime-like and Velcro-like adhesions were lost when SA and mannose were cleaved, respectively. While virus self-adhesion in forced contact was modulated by glycan penetrability, the self-aggregation of the freely diffusing virus was only determined by the surface sugar. Mannose-terminal viruses self-aggregated in solution, and SA-terminal ones required Ca ions to self-aggregate. Viruses with galactose or -acetylglucosamine surfaces did not self-aggregate, irrespective of whether or not a mannose core was present below the -acetylglucosamine surface. Well-defined rules appear to govern the self-adhesion and -aggregation of N-glycosylated surfaces, regardless of whether the sugars are presented in an ill-defined monolayer, or -glycan, or even polymer architecture.