Identifying conformational changes of aptamer binding to theophylline: A combined biolayer interferometry, surface-enhanced Raman spectroscopy, and molecular dynamics study.

Theophylline is a potent bronchodilator for the treatment of asthma, bronchitis, and emphysema. Its narrow therapeutic window (20-100 μM) demands that the blood concentration of theophylline be monitored carefully, which can be achieved by aptamer capture. Thus, an understanding of what occurs when aptamers bind to theophylline is critical for identifying a high-affinity and high-specificity aptamer, which improve the sensitivity and selectivity of theophylline detection. Consequently, there is an urgent need to develop a simple, convenient, and nondestructive method to monitor conformational changes during the binding process. Here, we report the determination of the affinity of a selected aptamer and theophylline via biolayer interferometry (BLI) experiments. Additionally, using surface-enhanced Raman spectroscopy (SERS), the conformational changes on theophylline-aptamer binding were identified from differences in the SER spectra. Finally, molecular dynamics (MD) simulations were used to identify the specific conformational changes of the aptamer during the binding process. Such a combined BLI-SERS-MD method provides an in-depth understanding of the theophylline-aptamer binding processes and a comprehensive explanation for conformational changes, which helps to select, design, and modify an aptamer with high affinity and specificity. It can also be used as a scheme for the study of other aptamer-ligand interactions, which can be applied to the detection, sensing, clinical diagnosis, and treatment of diseases.