Herein, we report a DNA nanodevice that autonomously and processively moves along a DNA track. The motion mechanism of this DNA device is reminiscent of that of singleheaded myosins I, a family of cellular protein motors. [1] The DNA device contains a DNA enzyme (DNAzyme) that constantly extracts chemical energy from its substrate molecules (RNA) and uses this energy to fuel the motion of the DNA device.
Nanomachines have potential applications in smart materials, sensors, and optoelectronic devices. [2] Many approaches have been explored to develop such nanomachines. By taking advantage of a rich body of knowledge of DNA biophysics, various DNA nanomachines have been rationally designed and built based on conformational changes. [3] The motions include opening/closure, extension/contraction, and rotation. More complex nanomechanical devices, such as walkers and gears, have also been demonstrated. [3l,m,o] However, such devices need human intervention for each step of their motions. The DNA structures change only once when the conditions of the solution are changed or a DNA strand is added. These DNA devices are in sharp contrast with cellular protein motors and manmade machines at the macroscale, both of which can continuously work without human interference.
An autonomous DNA motor has recently been reported [3k,n] -here we refer to "autonomous" as being selfcontained and not requiring human interference or other external active components such as protein enzymes. The motor performs an extremely simple motion: open and close. In a related, autonomous system, a DNA fragment could be continuously translocated along one direction by natural proteins (a combination of a DNA ligase and two restriction endonucleases). [3o] Logically, we wondered if it is possible to construct a more sophisticated, self-contained autonomous motor that could constantly walk or rotate. Herein, we demonstrate that such a machine is feasible.
The walking mechanism of the new system integrates DNAzyme activity and a strand-displacement strategy (Figure 1). The system consists of a walker and a track: The walker is a 10-23 DNAzyme, E, [4] which is a DNA molecule that can cleave RNA with sequence specificity (Figure 1 A).