title: Artificial G-wire switch with 2,2'-bipyridine units responsive to divalent metal ions.
abstract: Development of a guanine nanowire (G-wire) that is controllable and can be switched by external signals is important for the creation of molecular electronic technologies. Here, we constructed a G-wire in which the thymines of the main chain of d(G4T4G4) were replaced with 2,2'-bipyridine units, which have two aromatic rings that rotate arbitrarily upon coordination with metal ions. Circular dichroism of the DNA oligonucleotides with or without the 2,2'-bipyridine unit showed that divalent metal ions induce the bipyridine-containing oligonucleotide to switch from an antiparallel to a parallel G-quadruplex. Native polyacrylamide gel electrophoresis showed that the parallel-stranded G-quadruplex DNA had a high-order structure. Circular dichroism and native gel electrophoresis analyses suggested that adding Na2EDTA causes a reverse structural transition from a parallel-stranded high-order structure to an antiparallel G-quadruplex. Moreover, atomic force microscopy showed a long nanowire ( approximately 200 nm) in the presence of Ni2+ but no significant image in the absence of Ni2+ or in the presence of both Ni2+ and Na2EDTA. These observations revealed that the parallel-stranded high-order structure is a G-wire containing numerous DNA oligonucleotide strands bound together via divalent metal ion-2,2'-bipyridine complexes. Finally, we found that alternating addition of Ni2+ and Na2EDTA can cycle the G-wire between the high-order and disorganized structures, with an average cycling efficiency of 0.95 (i.e., 5% loss per cycle). These results demonstrate that a DNA oligonucleotide incorporating the 2,2'-bipyridine unit acts as a G-wire switch that can be controlled by chemical input signals, namely, divalent metal ions.
authors: Frontier Institute for Biomolecular Engineering Research, and Department of Chemistry, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Higashinada-ku, Kobe, Japan.
authors: Daisuke
authors: D
authors: Miyoshi
authors: Hisae
authors: H
authors: Karimata
authors: Zhong-Ming
authors: ZM
authors: Wang
authors: Kazuya
authors: K
authors: Koumoto
authors: Naoki
authors: N
authors: Sugimoto
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D018625:Microscopy, Atomic Force; D053770:Nanowires; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet
chemical_list: D015082:2,2'-Dipyridyl; D004247:DNA