Mannose Surfaces Exhibit Self-Latching, Water Structuring, and Resilience to Chaotropes: Implications for Pathogen Virulence.

Several viral and fungal pathogens, including HIV, SARS, Dengue, Ebola, and Cryptococcus neoformans, display a preponderance of mannose residues on their surface, particularly during the infection cycle or in harsh environments. The innate immune system, on the other hand, abounds in mannose receptors which recognize mannose residues on pathogens and trigger their phagocytosis. We pose the question if there is an advantage for pathogens to display mannose on their surface, despite these residues being recognized by the immune system. The surface properties and interactions of opposing monolayers of mannobiose (disaccharide of mannose) were probed using atomic force spectroscopy. Unlike its diastereoisomer lactose, mannobiose molecules exhibited lateral packing interactions that manifest on the surface scale as a self-recognizing latch. A break-in force is required for opposing surfaces to penetrate and a breakout (or self-adhesion force) of similar magnitude is required for penetrated surfaces to separate. A hierarchy of self-adhesion forces was distinguished as occurring at the single residue (∼25 pN), cluster (∼250 pN), monolayer (∼1.1 nN), and supramonolayer level. The break-in force and break-out force appear resilient to the presence of simple chaotropes that attenuate a layer of structured water around the mannose surface. The layer of structured water otherwise extends to distances several times longer than a mannobiose residue, indicating a long-range propagation of the hydrogen bonding imposed by the residues. The span of the structured water increases with the velocity of an approaching surface, similar to shear thickening, but fissures at higher approach velocities. Our studies suggest that mannose residues could guide interpathogen interactions, such as in biofilms, and serve as a moated fortress for pathogens to hide behind to resist detection and harsh environments.