Nanotechnology sticks its neck out

(Photo by David Bradley)Materials scientist Cyrus Safinya and biochemist Leslie Wilson at the University of California Santa Barbara have discovered quite by accident a “living necklace”, using synchrotron x-ray scattering techniques at the Stanford Synchrotron Radiation Laboratory combined with sophisticated electron and optical microscopy.

The scientists, including graduate student Daniel Needleman and postdoctoral researchers Uri Raviv, Miguel Ojeda-Lopez, and Herbert Miller, were studying microtubules from cow cells. Microtubules are hollow protein filaments used to transport chromosomes to each end of the cell during cell division, among other tasks. They also transport neurotransmitters in brain cells. Researchers do not yet understand how the cell constructs microtubules but a clearer perspective could lead to new treatments for numerous diseases.

Safinya and colleagues now report a higher order assembly of microtubules. He and his colleagues found that positively charged large, linear molecules (tri-, tetra-, and penta-valent cations) resulted in a tightly bundled hexagonal grouping of microtubules as expected. But, they also observed an unexpected result. They discovered that small, spherical divalent cations caused the microtubules to assemble into a “necklace” shape, with distinct linear, branched, and loop shaped necklaces.

The discovery of this living necklace phase of microtubule construction is the first experimental demonstration of a new type of membrane in which long microtubule molecules are oriented in the same direction but can diffuse within the living membrane. The researchers explain that the living necklace bundle is highly dynamic and changes shape when even slightly heated.

Credit: Cyrus Safinya/UCSB/PNAS

Credit: Cyrus Safinya/UCSB/PNAS

The next step is to modify the necklace bundles, perhaps by metallizing them to create novel materials with tunable optical properties. However, the team also suggests that the necklaces could have a more general use in encasing other compounds, such as a drug or a therapeutic gene. The material could then act as a transporter to carry the therapeutic gene into target cells.

Proc Natl Acad Sci, 2004;