The scientists at the University of California, Santa Barbara, used microtubules purified from the brain tissue of a cow for their experiments. Microtubules are nanometer-scale hollow cylinders derived from the cell cytoskeleton.
"In our paper, we report on a new paradigm for lipid self-assembly leading to nanotubule formation in mixed charged systems," said Cyrus R. Safinya, professor of materials and physics and faculty member of the Molecular, Cellular, and Developmental Biology Department.
Uri Raviv, a post-doctoral researcher in Safinya's lab, explained, "We looked at the interaction between microtubules - negatively charged nanometer-scale hollow cylinders derived from cell cytoskeleton - and cationic (positively charged) lipid membranes. We discovered that, under the right conditions, spontaneous lipid protein nanotubules will form."
The new type of self-assembly arises because of an extreme mismatch between the charge densities of microtubules and cationic lipid, explained Raviv. "This is a novel finding in equilibrium self-assembly," he said.
The nanotubule consisting of a three-layer wall appears to be the way the system compensates for this charge density mismatch, according to the authors. "Very interestingly, we have found that controlling the degree of overcharging of the lipid-protein nanotube enables us to switch between two states of nanotubes," said Safinya. "With either open ends (negative overcharged), or closed ends (positive overcharged with lipid caps), these nanotubes could form the basis for controlled chemical and drug encapsulation and release."
The inner space of the nanotube in these experiments measures about 16 nanometers in diameter. The whole capsule is about 40 nanometers in diameter.
MEDICA.de; Source: University of California, Santa Barbara