Molecular recognition based on low-affinity polyvalent interactions: Selective binding of a carboxylated polymer to fibronectin fibrils of live fibroblast cells

To explore molecular recognition of biomolecules in the complex environment of the extracellular matrix, we utilized two fluorescent poly (p-phenyleneethynylene)s bearing either cationic alkylammonium or negatively charged carboyxlate side chains. While incubation of live NIH 3T3 fibroblast cells with the cationic polymer yielded perinuclear punctate staining reminiscent of endocytotic vesicles, the carboxylated polymer revealed a characteristic filamentous staining pattern. Histochemical and immunofluorescence studies demonstrated that the anionic PPE selectively binds to fibronectin fibrils of the extracellular matrix. An in vitro binding study revealed a dissociation constant of approximately 100 nM for the fibronectin-polymer complex. Both polymers showed bright two-photon excited emission as well as low toxicity, rendering them well-suited for live cell imaging studies. The studies demonstrate that selective molecular recognition of biomolecules in the complex environment of the extracellular matrix can be achieved by means of nonspecific low-affinity polyvalent interactions.