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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-to-cell contact mediated by glycan:glycan interactions have been considered to be low-affinity interactions that precede high-affinity 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.

SUBMITTER: Day CJ

PROVIDER: S-EPMC4702957 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The mucin MUC16 and the glycosylphosphatidylinositol anchored glycoprotein mesothelin likely facilitate the peritoneal metastasis of ovarian tumors. The biochemical basis and the kinetics of the binding between these two glycoproteins are not clearly understood. Here we have addressed this deficit and provide further evidence supporting the role of the MUC16-mesothelin interaction in facilitating cell-cell binding under conditions that mimic the peritoneal environment.In this study we utilize recombinant-Fc tagged human mesothelin to measure the binding kinetics of this glycoprotein to MUC16 expressed on the ovarian tumor cell line OVCAR-3. OVCAR-3 derived sublines that did not express MUC16 showed no affinity for mesothelin. In a flow cytometry-based assay mesothelin binds with very high affinity to the MUC16 on the OVCAR-3 cells with an apparent Kd of 5-10 nM. Maximum interaction occurs within 5 mins of incubation of the recombinant mesothelin with the OVCAR-3 cells and significant binding is observed even after 10 sec. A five-fold molar excess of soluble MUC16 was unable to completely inhibit the binding of mesothelin to the OVCAR-3 cells. Oxidation of the MUC16 glycans, removal of its N-linked oligosaccharides, and treatment of the mucin with wheat germ agglutinin and erythroagglutinating phytohemagglutinin abrogates its binding to mesothelin. These observations suggest that at least a subset of the MUC16-asscociated N-glycans is required for binding to mesothelin. We also demonstrate that MUC16 positive ovarian tumor cells exhibit increased adherence to A431 cells transfected with mesothelin (A431-Meso+). Only minimal adhesion is observed between MUC16 knockdown cells and A431-Meso+ cells. The binding between the MUC16 expressing ovarian tumor cells and the A431-Meso+ cells occurs even in the presence of ascites from patients with ovarian cancer.The strong binding kinetics of the mesothelin-MUC16 interaction and the cell adhesion between ovarian tumor cells and A431-Meso+ even in the presence of peritoneal fluid strongly support the importance of these two glycoproteins in the peritoneal metastasis of ovarian tumors. The demonstration that N-linked glycans are essential for mediating mesothlein-MUC16 binding may lead to novel therapeutic targets to control the spread of ovarian carcinoma.

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

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