DNA gets hands and feet

Genetic robots take a walk.

DNA used to be the information molecule, leaving all the action to the proteins. Not any more. The genetic material has recently served to build complex structures, and now even machines with moving parts. Following the development of a medical device based on DNA (Chemistry World, June 2004, p25) researchers have fitted DNA with ’hands’ to hold and release things and ’feet’ for molecular walking tours.

Friedrich Simmel and colleagues at the University of Munich, Germany, designed a DNA hand that can be instructed to grasp and release a molecule of the enzyme thrombin.1 The device is based on a 15-base DNA sequence known to bind thrombin. ’We chose the thrombin aptamer because it was short, well-characterised and had a low dissociation constant,’ says Simmel. He combined this element with a 12-base tag that makes the hand controllable by additional DNA sequences. By adding a specific DNA molecule (Q) that recognises this tag, the researchers dislodged the bound enzyme. Another DNA sequence (R) outcompetes the hand in its interaction with Q, and thus sets it free to bind the enzyme again.

Meanwhile, William Sherman and Ned Seeman at the New York University, US, have built a walking DNA robot using a similar approach. Its two feet have different sequences, which recognise two kinds of foothold on the DNA track. Soluble DNA strands outcompete the binding interactions and help to get the DNA robot walking.

Simmel recognises that the ’hand’ and ’feet’ converge naturally: ’In combination with DNA walkers,’ he explains, ’our device could form the carrying part of a DNA motor which grabs a molecule in one place and releases it in another. Similar devices could be constructed which bind or release nonbiological molecules rather than proteins.’ Further research from Simmel’s laboratory even shows that DNA machines can be controlled biologically, via the cell’s transcription process. With DNA robots evolving at that pace, can it be long before they start to talk and serve drinks?

Michael Gross