Glycan:glycan interactions: High affinity biomolecular interactions that can mediate binding of pathogenic bacteria to host cells

Abstract

Cells from all domains of life express glycan structures attached to lipids and proteins on their surface, called glycoconjugates. Cell-tocell contact mediated by glycan:glycan interactions have been considered to be low-affinity interactions that precede highaffinity protein-glycan or protein-protein interactions. In several pathogenic bacteria, truncation of surface glycans, lipooligosaccharide (LOS), or lipopolysaccharide (LPS) have been reported to significantly reduce bacterial adherence to host cells. Here, we show that the saccharide component of LOS/LPS have direct, high-affinity interactions with host glycans. Glycan microarrays reveal that LOS/LPS of four distinct bacterial pathogens bind to numerous host glycan structures. Surface plasmon resonance was used to determine the affinity of these interactions and revealed 66 high-affinity host-glycan:bacterial-glycan pairs with equilibrium dissociation constants (K D ) ranging between 100 nM and 50 μM. These glycan:glycan affinity values are similar to those reported for lectins or antibodies with glycans. Cell assays demonstrated that glycan:glycan interaction-mediated bacterial adherence could be competitively inhibited by either host cell or bacterial glycans. This is the first report to our knowledge of high affinity glycan:glycan interactions between bacterial pathogens and the host. The discovery of large numbers of glycan:glycan interactions between a diverse range of structures suggests that these interactions may be important in all biological systems.H ost surface glycosylation is ubiquitous and is targeted by pathogenic bacteria, viruses, fungi and parasites for adherence and toxin binding and by glycosidases (1). Escherichia coli type 1 fimbriae, FimH, is one of the most widely studied glycanrecognizing protein adhesins, with specificity for monomannose to oligomannose structures with the variability of the mannose structure bound leading to different tissue tropism (2). Other glycan-recognizing adhesins expressed by bacteria include the following: Pseudomonas aeruginosa lectins 1 and 2 (PA-IL and PA-IIL) that have specificity for galactose and fucose, respectively (3); Helicobacter pylori SabA, specific for sialic acid containing glycoconjugates including sialyLewis X; and BabAspecific for fucosylated glycoconjugates including Lewis B (4, 5). Although there are numerous known glycan binding adhesins, the adhesins of some bacteria that interact with host surface glycans remain unknown.Direct interactions between surface glycans (glycan:glycan interactions) have been reported in sea sponges as heterogenous glycan interactions, and in mouse embryo development and cancer where homodimers of Lewis X (LeX) or ganglioside structures play a role in cell adhesion and growth factor receptor interactions (6, 7). Outside of these reports, glycan:glycan interactions, when noted, have generally been considered to be low-affinity, weak interactions (8) that precede high-affinity protein:glycan or protein:protein interactions (1, 2, 5, 9).Interestingly, there...

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“…This is in agreement with the role of N-glycans of integrins (Janik et al, 2010;Gu et al, 2012), which are transmembrane proteins involved in mechanotransduction by facilitating interactions with the ECM (Schwartz, 2010). The proposed new role of N-glycans as facilitators of mechanical activation of ion channels is also supported by studies identifying that glycan/glycan interactions provide a high binding strength that facilitates binding of bacteria to host cells (Day et al, 2015), but also cell adhesion in multicellular organisms (Popescu et al, 2003).…”

A facile method for cellular N-glycomic profiling by matrix-assisted laser desorption/ionization mass spectrometry

“…Almost all membrane and secreted proteins of mammals, 1 as well as numerous cytoplasm and nucleus proteins [2][3][4] are glycosylated. It has been well documented that N-glycans play crucial roles in many biological processes such as cell growth and development, 5,6 immune recognition, 7-9 cell-cell communication, 10 infectivity of many pathogenic bacteria 11,12 and most viruses.…”

Analysis of Bacterial Lipooligosaccharides by MALDI-TOF MS with Traveling Wave Ion Mobility

“…The carbohydrate moieties of LOS are antigens presented on the bacterial cell surface that can interact with host proteins [15] and host glycans [16]. Some LOS carbohyd r a t e m o i e t i e s m i m i c h u m a n g l y c o l i p i d a n d glycosphingolipid structures [17,18].…”