Cationic Liposome-Microtubule Complexes: Pathways to the Formation of Two-State Lipid-Protein Nanotubes with Open or Closed Ends
Cationic Liposome-Microtubule Complexes: Pathways to the Formation of Two-State Lipid-Protein Nanotubes with Open or Closed Ends.
Uri Raviv, Daniel J. Needleman, Miguel Ojeda-Lopez, Herbert P. Miller, Leslie Wilson, Cyrus R. Safinya
Proceedings of the National Academy of Sciences, Track II, August 2005, 102, 11167-11172
Soft matter keywords: polyelectrolyte lipid complex, membrane, tubulin, vesicles, "beads on a rod"
Interactions between electrically charged lipids and biopolymers are utilized for numerous cell processes, such as transporting the contents of vesicles into a cell (e.g. endocytosis, drug delivery, and gene therapy). The present study examines a range of cationic lipids with anionic tublin dimers. Previous researchers studied two different cases of interactions.
- If the membrane curvature is zero, a multilamellar phase forms, with the polyelectroytle trapped in chains between layers of the lipid.
- If the membrane has a negative spontaneous curvature, an inverted hexagonal phase forms, in which the lipids form tubes arranged in a heaxgonal lattice around chains of the polyelectrolyte.
In the present study, the authors examine the case when the spontaneous curvature of the lipid membrane is comparable to the "curvature" of the tubulin molecules (twice the reciprocal of the polyelectrolyte diameter). Depending on the relative concentrations of lipids and tubulin molecules, a nanotububle forms with either open or closed ends. Since positively charged lipids are commonly used for encapsulating genes and drugs into cells, the results from the present study could be extended to novel, non-viral delivery systems.
Soft Matter Concepts
The present study is an example of exploring the phase space of a liposome-microtubule complex. The lipids are positively charged and interact electro-statically with negatively charged tubulin molecules. By varying the rigidity of the components, the charge density of the membrance, and the ratio of charged lipids to tubulin dimers, an assortment of shapes can be produced, as illustrated in the flow chart below:
written by: Naveen N. Sinha