'Frankly, some researchers didn't
think what we were doing was possible,' says Dr Keith
Firman, on the completion of the Sixth Framework
Programme (FP6) Mol-Switch project that he coordinates.
'However, we got our molecular switch to work,' he
told IST Results.
The project has not just worked, but has succeeded under intense scrutiny and
scepticism from experts in associated fields, such as biotechnology and biophysics.
The project itself is rather difficult to conceptualise: a 'nano-actuator' device
so small that it could be used to move specific DNA fragments, and allow individual
DNA sequencing. The project's aim was to produce an individual molecular 'nano-switch'.
Six partners, the University of Portsmouth, UK; the National Physical Laboratory,
UK; ENS/CNRS, France; TUDelft, the Netherlands; the University of Parma, Italy
and the Institute of Microbiology in Prague, the Czech Republic, developed the
nano-device over three years.
It was decided beforehand that the project would be considered a success if it
could demonstrate the activity, efficiency and stability of the switch, its effectiveness
at DNA sequencing, and its commercial potential.
The experimental part of the project had two phases - firstly, to use a biological
motor to produce a nanoactuator (or simply a device) which would pull a magnetic
bead towards a surface. The movement of the bead would generate a tiny, but detectable,
Secondly, the biological motor should pull fluorescently-labelled DNA towards
a fluorescently-labelled version of the motor. This will result in 'Fluorescent
Resonant Energy Transfer' (FRET), which can give accurate measurements of the
DNA sequencing, and therefore the switch's accuracy.
DNA sequencing is what the Human Genome project was set up to decode in the human
body. DNA has four 'bases' within it. These bases are all proteins, identified
by the letters A, C, G and T. Different gene sequences are simply lists of A,
C, G and T in different combinations.
The researchers used a type of molecular motor known as a 'Restriction-Modification
enzyme'. This molecular motor attaches itself only to specific sequences of A,
C, G and T. 'This binding is very specific, a motor will bind only with its corresponding
bases, so you can control exactly where the motor is placed on the vertical DNA
strand,' said Dr Firman.
The DNA strand is held upright by a magnetic field, pulling a magnetic marker
at the end of the DNA strand. The molecular motor sits somewhere below the magnetic
marker at a specific position, and does not move. When the molecular engine is
started, when fed biological fuel ATP, it pulls the DNA strand, stopping when
it reaches the magnetic marker.
Why does this matter, and what use is this? Most simply, this nano-switch enables
one form of energy to be transferred to another for a useful purpose, and in
a controlled fashion. 'The light switch, the button that makes a retractable
pen, all these are actuators, and by developing a molecular switch we've created
a tiny actuator that could be used in an equally vast number of applications,'
says Dr Firman.
The result is quite literally a building-block for the nano-world, and as the
imaginations of researchers grow, so will useful applications of the switch.
'It could be used as a communicator between the biological and silicon worlds.
I could see it providing an interface between muscle and external devices, through
its use of ATP, in human implants. Such an application is still 20 or 30 years
away,' says Dr Firman 'It's very exciting and right now we're applying for a
patent for the basic concepts.'
One unintended by-product of this research is in DNA sequencing. If the DNA strand
is marked with fluorescence, then 'Knowing the speed of the motor, which is quite
reliable and steady at any specific temperature, we could locate the position
of the DNA-based Fluor [molecule] relative to the binding site of the motor,'
says Dr Firman. 'More work needs to be done. However, the concept is sound and
we now have enough evidence to indicate that this could be used to sequence single-nucleotide
polymorphisms (SNPs) that cause genetic disorders.'
The next step is to turn this idea into a marketable product. 'We're applying
for a new project under the [European Union's] New and Emerging Science and Technology
(NEST) scheme and, if that's successful, we will be able to develop a commercial
product for biosensing,' says Dr Firman.
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