LAUSR

Owing to its great threat to human health and environment, Pb 2+ 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 2+ -detection sensors, but the underlying mechanisms remain elusive. Here, we report three Pb 2+ -complexed structures of the thrombin binding aptamer (TBA). These high-resolution crystal structures showed that TBA forms intramolecular G-quadruplex and Pb 2+ is bound by the two G-tetrads in the center. Compared to K + -stabilized G-quadruplexes, the coordinating distance between Pb 2+ 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 2+ -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 2+ -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.