Investigations of molecular interactions at the chemistry-biology interface: The design of interfacial biomaterials and the modulation of galectin-3 aggregation with multivalent saccharide ligands

Myriad biological processes are governed by chemical reactions that occur on cell surfaces. Cellular communication, transportation and recognition are all chemically-mediated processes that occur at the cell-cell interface. While 'interface' describes the physical area of contact between cellular systems, it also describes the area of study that coalesces between the traditional disciplines of chemistry and biology. Utilizing chemical and biological techniques, two approaches are presented that investigate the mechanisms of molecular interactions at biological interfaces.;In the first part of this work, a novel approach to direct biological processes that occur at the surface of artificial materials is described. Many biomedical implants are hindered by overly robust fibrotic and inflammatory responses that compromise the function of the device. A material that can promote cellular adhesion and tissue development at the material-biologic interface would reduce the potential for an adverse response. A multi-faceted strategy has been developed to construct 'interfacial biomaterials' (IFBMs) that mediate specific biological processes via increased cellular adhesion to medically-relevant materials. We have developed a combinatorial phage display selection strategy to identify peptides that show increased affinity for natural and artificial substrates. Peptides specific to both stainless steel and polycarbonate were identified by this methodology. IFBMs containing a stainless steel-binding peptide and an osteoblast-specific tetrapeptide were chemically synthesized for cell-culture studies. In vitro, the coatings significantly enhanced osteoblast adhesion to treated surfaces in both overnight and three-day cultures.;In the second part of this work, the molecular basis of protein-carbohydrate binding is considered. Galectin-3 is a protein that shows natural affinity for β-galactosides, specifically lactose and LacNAc. Mono-, bi-, and trivalent ligands displaying lactose epitopes were constructed to investigate their aggregative properties towards full-length galectin-3 and truncated carbohydrate recognition domain (CRD). Isothermal titration calorimetry studies with full-length protein shows a greater than two-fold binding enhancement in affinity for the bivalent ligand compared to monovalent ligand. The same bivalent ligand shows no enhancement when binding the truncated CRD. This observation supports the hypothesis that the N-terminal domain present in galectin-3 promotes aggregation in aqueous solution. This behavior also demonstrates unequivocally that protein-protein interactions and aggregation are the primary cause for affinity increases observed with polyvalent saccharide ligands, and unambiguously establishes a molecular basis for the cluster glycoside effect.