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The STUDIA UNIVERSITATIS BABEŞ-BOLYAI issue article summary
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Abstract: Cellular interactions involve many types of cell surface molecules operating via homophilic and/or heterophilic protein-protein and protein-carbohydrate binding. Our investigations using the marine sponge Microciona prolifera as a model system have provided direct evidence that a novel class of primordial proteoglycans, named by us glyconectins, can mediate cell adhesion via a new alternative molecular mechanism of polyvalent carbohydrate-carbohydrate binding. Biochemical characterisation of purified glyconectins revealed the presence of specific acidic glycans different from classical glycosaminoglycans. These glyconectins mediate in vivo cell recognition and aggregation via homophilic, species-specific, polyvalent, and calcium ion-dependent glycan-glycan interactions. The kinetic binding studies, calorimetric methods, X-ray diffraction, nuclear magnetic resonance, and other spectroscopic analyses do not supply a direct estimation of the intermolecular binding forces that are fundamental for the function of the ligand-receptor association. Recently, we have introduced atomic force microscopy to quantify the binding strength between cell adhesion proteoglycans. Measurement of binding forces intrinsic to cell adhesion molecules is necessary to assess their contribution to the maintenance of the anatomical integrity of multicellular organisms. As a model, we selected the glyconectin 1, a cell adhesion proteoglycan isolated from the marine sponge Microciona prolifera. Under physiological conditions, an adhesive force of up to 400 piconewtons between two cell glyconectins was measured. Such a large cohesive force as this is theoretically able to hold the weight of approximately 1600 cells in physiological solution. Thus the integrity of the multicellular sponge organism, with at least 1000 glyconectin molecules per cell, may be maintained by the multiplicity of glyconectin-glyconectin interactions. Our results suggest that the strength and polyvalency of glycan-glycan interactions are essential for cell adhesion. |
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