First DNA rotaxane

The first example of a rotaxane molecule made from DNA has been constructed by German chemists. Rotaxanes are dumbbell-shaped molecules encircled by a molecular hoop that can move unhindered along the axle, trapped by the bulky stoppers at either end. DNA rotaxanes could prove to be useful components in molecular machines.

To make the molecules, Michael Famulok’s team at the University of Bonn exploited the natural propensity of single-stranded DNA to ’stick’ to a complementary sequence of single-stranded DNA to create double-stranded DNA. They constructed a hoop of double-stranded DNA which contained a small gap consisting of a single-strand. They then created a length, or axle, of double-stranded DNA which also had a single-stranded gap, whose sequence was complementary to that in the hoop. When the two were brought into contact the complementary single-stranded regions attached spontaneously, sticking the hoop to the middle of the axle.

Bulky DNA ’stoppers’ were then attached to either end of the axle creating a pseudorotaxane - with the axle and hoop still attached to each other. Adding a short length of nucleotides of appropriate sequence to the system, frees the hoop from the axle creating a true rotaxane.

DNA rotaxanes are attractive as components for molecular machines, says Famulok. ’It would be interesting to see if we could immobilise the axle part of the molecule then somehow rotate the ring, which would produce a spinning wheel.’ It would be relatively simple to attach functional groups to various parts of the structure, further increasing the system’s versatility. ’Also DNA rotaxanes can be made much larger than conventional organic rotaxanes, giving greater margins for parts to move,’ Famulok adds. 

Because of the simplicity of the construction method, multiple configurations of rings and axles should be possible - with several rings encircling a single axle or vice versa, for example.

Jonathan Bath, who researches DNA nanostructures at the University of Oxford in the UK, is impressed with the work. ’I like it - it is an elegant paper,’ he says.

Simon Hadlington