Ion-responsive hemin-G-quadruplexes for switchable DNAzyme and enzyme functions.

Programmed nucleic acid sequences undergo K(+) ion-induced self-assembly into G-quadruplexes and separation of the supramolecular structures by the elimination of K(+) ions by crown ether or cryptand ion-receptors. This process allows the switchable formation and dissociation of the respective G-quadruplexes. The different G-quadruplex structures bind hemin, and the resulting hemin-G-quadruplex structures reveal horseradish peroxidase DNAzyme catalytic activities. The following K(+) ion/receptor switchable systems are described: 1) The K(+) -induced self-assembly of the Mg(2+) -dependent DNAzyme subunits into a catalytic nanostructure using the assembly of G-quadruplexes as bridging unit. 2) The K(+) -induced stabilization of the anti-thrombin G-quadruplex nanostructure that inhibits the hydrolytic functions of thrombin. 3) The K(+) -induced opening of DNA tweezers through the stabilization of G-quadruplexes on the "tweezers' arms" and the release of a strand bridging the tweezers into a closed structure. In all of the systems reversible, switchable, functions are demonstrated. For all systems two different signals are used to follow the switchable functions (fluorescence and the catalytic functions of the derived hemin-G-quadruplex DNAzyme).