UC Santa Barbara researchers discover living nanoscale 'necklace'

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UC Santa Barbara researchers discover living nanoscale 'necklace'

09 Nov 2004 http://www.medicalnewstoday.com/medicalnews.php?newsid=16073

In an interdisciplinary endeavor at the University of California, Santa

Barbara, a team of researchers in physics and biology have made a

discovery at the nanoscale level that could be instrumental in the

production of miniaturized materials with many applications. Dubbed a

" living necklace, " the finding was completely unexpected.

This discovery could influence the development of vehicles for chemical,

drug, and gene delivery, enzyme encapsulation systems and biosensors,

circuitry components, as well as templates for nanosized wires and

optical materials. The findings are reported in the November 16 issue of

the Proceedings of the National Academy of Sciences and published online

the week of November 8.

The collaborating labs are those of Cyrus Safinya, professor of

materials and physics and faculty member of the Biomolecular Science &

Engineering Program, and , professor of biochemistry in the

Department of Molecular, Cellular and Developmental Biology. The first

author of the paper is Safinya's graduate student Needleman.

Postdoctoral researchers Uri Raviv and Ojeda- from Safinya's

group and Herbert , a researcher in 's group, completed the

team.

The scientists studied microtubules from the brain tissue of a cow to

understand the mechanisms leading to their assembly and shape.

Microtubules are nanometer-scale hollow cylinders derived from cell

cytoskeleton. In an organism, microtubules and their assembled

structures are critical components in a broad range of cell functions --

from providing tracks for the transport of cargo to forming the spindle

structure in cell division. Their functions include the transport of

neurotransmitters in neurons. The mechanism of their assembly within an

organism has been poorly understood.

In the paper, the researchers report the discovery of a new type of

higher order assembly of microtubules. Positively-charged large, linear

molecules (tri-, tetra- and penta-valent cations) resulted in a tightly

bundled hexagonal grouping of microtubules - a result that was

predicted. But unexpectedly, the scientists found that small, spherical

divalent cations caused the microtubules to assemble into a " necklace. "

They discovered distinct linear, branched and loop shaped necklaces.

Safinya and Needleman commented that from a formal theoretical physics

perspective, the living necklace phase is the first experimental

realization of a new type of membrane where the long microtubule

molecules are oriented in the same direction but can diffuse within the

living membrane.

They explained that the living necklace bundle is highly dynamic and

that thermal fluctuations will cause it to change shape.

The scientists envision applications based on both the tight bundle and

living necklace phases. For example, metallization of necklace bundles

with different sizes and shapes would yield nanomaterials with

controlled optical properties.

A more original application is in the area of using the assemblies -

encased by a lipid bilayer - as drug or gene carriers where each

nanotube may contain a distinct chemical, as noted by the team. In

delivery applications the shape of the bundle determines its property.

For example, the linear necklace phase with its higher surface to volume

ratio would have a larger contact area and a faster delivery rate

compared to the tight bundle phase.

The work was performed using state-of-the-art synchrotron x-ray

scattering techniques at the Stanford Synchrotron Radiation Laboratory

combined with sophisticated electron and optical microscopy at UCSB.