Optical emission of a conjugated polyelectrolyte:: Calcium-induced conformational changes in calmodulin and calmodulin-calcineurin interactions

Electronic polymers in aqueous media offer bioelectronic detection of biomolecular processes. Here we report fluorometric detection of calcium-induced conformational changes in calmodulin based on noncovalent assembly of calmodulin to a water-soluble zwitterionic polythiophene derivative. Assembly with calmodulin will induce a planar geometry and aggregation of the polymer chains, detected as a decrease of the intensity and a red shift of the fluorescence. Upon addition of Ca2+ the intensity of the emitted light is increased and blue-shifted. The geometrical alteration of the polymer chains can further be utilized for recording of the binding of calcineurin to the calcium-activated POWT-calmodulin complex. This novel methodology, using a conformation-sensitive probe, allows fluorometric detection of conformational changes in biomolecules and protein-protein interactions without any covalent modifications of the biomolecules. The rapid and selective method is based on noncovalent interactions between a zwitterionic polythiophene derivative and the biomolecule of interest. This offers a novel way to create microarrays without using covalent attachment of the receptor or labeling of the analyte.