DNA nanomachines and nanostructures involving quadruplexes.

DNA is an attractive component for molecular recognition, because of its self-assembly properties. Its three-dimensional structure can differ markedly from the classical double helix. For example, DNA or RNA strands carrying guanine or cytosine stretches associate into four-stranded structures called G-quadruplexes or i-DNA, respectively. Since 2002, several groups have described nanomachines that take advantage of this structural polymorphism. We first introduce the unusual structures that are involved in these devices (i.e., i-DNA and G-quadruplexes) and then describe the opening and closing steps that allow cycling. A quadruplex-duplex molecular machine is then presented in detail, together with the rules that govern its formation, its opening/closing kinetics and the various technical and physico-chemical parameters that play a role in the efficiency of this device. Finally, we review the few examples of nanostructures that involve quadruplexes.