In an interdisciplinary endeavor at the University of California Santa Barbara (UCSB), 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 unexpected finding 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. Using bovine brain tissue, the researchers studied nanometer-scale hollow cylinders derived from cell cytoskeleton, microtubules, to understand the mechanisms leading to their assembly and shape. 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 to aiding in the transport of neurotransmitters. However, the mechanism of their assembly within an organism has been poorly understood. In a recent paper in the Proceedings of the National Academy of Sciences, the researchers report the discovery of a new type of higher order assembly of microtubules. Unexpectedly, they found that small, spherical divalent cations caused microtubules to assemble into a "necklace." They discovered distinct linear, branched and loop shaped necklaces. 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. The team explained that the living necklace bundle is highly dynamic and that thermal fluctuations will cause it to change shape. Based on both the tight bundle and living necklace phases, they envision broad applications from nanomaterials with controlled optical properties to drug or gene carriers (using the assemblies encased by a lipid bilayer where each nanotube may contain a distinct chemical). This work was performed using SSRL Beam Line 4-2 as well as the electron and optical microscopy at UCSB. The research was supported by the National Science Foundation, the National Institutes of Health, and the Department of Energy.

The research was supported by the National Science Foundation, the National Institutes of Health, and the Department of Energy.

PNAS. 2004 Nov 16; 101(no. 46):16099-16103