title: Single-molecule detection of folding and unfolding of the G-quadruplex aptamer in a nanopore nanocavity.
abstract: Guanine-rich nucleic acids can form G-quadruplexes that are important in gene regulation, biosensor design and nano-structure construction. In this article, we report on the development of a nanopore encapsulating single-molecule method for exploring how cations regulate the folding and unfolding of the G-quadruplex formed by the thrombin-binding aptamer (TBA, GGTTGGTGTGGTTGG). The signature blocks in the nanopore revealed that the G-quadruplex formation is cation-selective. The selectivity sequence is K(+) > NH(4)(+) approximately Ba(2+) > Cs(+) approximately Na(+) > Li(+), and G-quadruplex was not detected in Mg(2+) and Ca(2+). Ba(2+) can form a long-lived G-quadruplex with TBA. However, the capability is affected by the cation-DNA interaction. The cation-selective formation of the G-quadruplex is correlated with the G-quadruplex volume, which varies with cation species. The high formation capability of the K(+)-induced G-quadruplex is contributed largely by the slow unfolding reaction. Although the Na(+)- and Li(+)-quadruplexes feature similar equilibrium properties, they undergo radically different pathways. The Na(+)-quadruplex folds and unfolds most rapidly, while the Li(+)-quadruplex performs both reactions at the slowest rates. Understanding these ion-regulated properties of oligonucleotides is beneficial for constructing fine-tuned biosensors and nano-structures. The methodology in this work can be used for studying other quadruplexes and protein-aptamer interactions.
authors.affiliation: Department of Biological Engineering, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA.
authors.forename: Ji Wook
authors.initials: JW
authors.lastname: Shim
authors.forename: Qiulin
authors.initials: Q
authors.lastname: Tan
authors.forename: Li-Qun
authors.initials: LQ
authors.lastname: Gu
mesh_terms: D052157:Aptamers, Nucleotide / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D054856:G-Quadruplexes; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry*
chemical_list: D052157:Aptamers, Nucleotide; D002412:Cations; C081676:thrombin aptamer