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|Posted: Wed Apr 02, 2008 3:00 pm Post subject: Proteins get ordered on the nanoscale
|6 July 2007 NanoTechWeb
Proteins get ordered on the nanoscale
Researchers in the UK have discovered a way to engineer nanoscale order into protein fibres for the first time. Derek Woolfson of the University of Bristol and colleagues adapted a system consisting of two peptides, which normally co-assemble into thick protein fibres in water, so that they showed a level of order on the nanoscale that mimics certain natural fibrous assemblies. The technique could be a way of building nanostructured biomaterials from the bottom up, for applications in synthetic biology and nanobiotechnology.
Woolfson's team designed a first-generation self-assembling fibre (SAF) made of two complementary “leucine-zipper” peptides a few years ago. To their surprise, the building blocks not only gave long thin fibril structures, but these thickened to give fibres that contained several hundred fibrils bundled together. "We explored the cause of this bundling and discovered that we could engineer the fibril–fibril interactions so that considerable nanoscale order could be introduced into the system," Woolfson told nanotechweb.org. "That is, we could 'cement' very specific fibril–fibril interactions."
In Woolfson's original design the complementary leucine-zipper peptides were engineered to combine to form a staggered dimer, like two Lego bricks stuck together offset. This is unlike natural structures that use the same building blocks, which come together "blunt ended". The staggered dimers form the building blocks of the fibrils because the overhanging ends are "sticky" for each other.
In the new work, Woolfson's team turned its attention to the outer faces of the fibrils and engineered complementary charged interactions to bring more fibrils together and thicken the fibres. "The surprise was that this also seemed to bring the fibrils together in a precise parallel and ordered manner," said Woolfson.
Using electron microscopy and X-ray diffraction, the researchers found that the peptides in the engineered system assembled into two-stranded alpha-helical coiled rods that pack into a 3D hexagonal lattice around 1.8 nm in size. The rods were separated by 4.2 nm along the fibre axis, precisely matching the lengths of the designed peptides. "This second level of order is observed as clear striations that run orthogonal to the long fibre axis," explained Woolfson. "These striations run the whole length of the fibres, which are up to tens of microns, indicating the fibres show crystalline coherence throughout their structure."
The spacing of the striations can be controlled simply by changing the length of the peptides. "To our knowledge, this exceptional order, its persistence along and across the fibres, and our ability to engineer it are unique in a biomimetic system," said the researchers.
"The protein fibres could be used as a scaffold to display other functional biomolecules with nanoscale precision, or more generally as a biocompatible scaffold to support cell growth and tissue engineering," enthused Woolfson.
Ultimately, the team would like to design atomic structures using its technique but this will be difficult, admits Woolfson. "We will work on this but our next step is going to move into 'decorating' the fibres with biological, inorganic and polymeric materials. We hope these hybrids will bring added function to the fibres."
Story posted: 26th July 2007