Structure-guided development of Pb-binding DNA aptamers.

Owing to its great threat to human health and environment, Pb pollution has been recognized as a major public problem by the World Health Organization (WHO). Many DNA aptamers have been utilized in the development of Pb-detection sensors, but the underlying mechanisms remain elusive. Here, we report three Pb-complexed structures of the thrombin binding aptamer (TBA). These high-resolution crystal structures showed that TBA forms intramolecular G-quadruplex and Pb is bound by the two G-tetrads in the center. Compared to K-stabilized G-quadruplexes, the coordinating distance between Pb and the G-tetrads are much shorter. The T3T4 and T12T13 linkers play important roles in dimerization and crystallization of TBA, but they are changeable for Pb-binding. In combination with mutagenesis and CD spectra, the G8C mutant structure unraveled that the T7G8T9 linker of TBA is also variable. In addition to expansion of the Pb-binding aptamer sequences, our study also set up one great example for quick and rational development of other aptamers with similar or optimized binding activity.