Ligand-Induced Folding in a Dopamine-Binding DNA Aptamer

Aptamers are often employed as a molecular recognition element in the development of different types of biosensors. Many of these biosensors take advantage of the aptamer having a ligand induced structure-formation binding mechanism. However, this binding mechanism is poorly understood. Here we use isothermal titration calorimetry and NMR spectroscopy to study the binding and ligand-induced structural change exhibited by the dopamine-binding DNA aptamer. We analysed a series of aptamers where we shorten the terminal stem that contains the 5’ and 3’ termini of the aptamer sequence. All aptamers bind dopamine in an enthalpically driven process compensated by an unfavorable entropy. A general trend of the aptamer having a weaker binding affinity is observed as the terminal stem is shortened. For all aptamers studied, numerous signals appear in the imino region of the 1H NMR spectrum indicating that new structure forms with ligand binding. However, it is only when this region of structure formation in the aptamer is brought close to the sensor surface that we obtain a functional electrochemical aptamer-based biosensor.