Microtubules, 25 nanometer scale hollow tubules, are critical components in a broad range of functions in eukaryotic cells -- from providing tracks for the transport of cargo to forming the spindle structure for chromosome segregation before cell division. They are used as nanometer scale tracks in neurons for the transport of neurotransmitter precursors and enzymes to synaptic junctions in nerve cell communication.

A group of researchers from the University of California at Santa Barbara have recently reported in the Proceedings of the National Academy of Sciences USA (vol. 102, no. 32, 11167-11172, 2005) on a new paradigm for lipid self-assembly leading to nanotubule formation in mixed charged systems with potential applications in gene and drug delivery. The bio-nanotubule results from the interaction between microtubules, which are overall negatively charged and cationic lipid membranes. Combining sophisticated analysis of SSRL synchrotron x-ray scattering data with high-resolution transmission electron microscopy elucidated the precise structure of the lipid-protein nanotube.

Significantly, controlling the degree of overcharging of the lipid-protein nanotube enables one to switch between two states of the nanotubes with either open or closed ends, which forms the basis for controlled chemical and drug or therapeutic nucleic acid encapsulation and release. The research was supported by the National Science Foundation and the National Institutes of Health.