Nanoscale assembly in biological systems: From neuronal cytoskeletal proteins to curvature stabilizing lipids

The review will describe experiments inspired by the rich variety of bundles and networks of interacting microtubules (MT), neurofilaments, and filamentous-actin in neurons where the nature of the interactions, structures, and structure-function correlations remain poorly understood. We describe how three-dimensional (3D) MT bundles and 2D MT bundles may assemble, in cell free systems in the presence of counter-ions, revealing structures not predicted by polyelectrolyte theories. Interestingly, experiments reveal that the neuronal protein tau, an abundant MT-associated-protein in axons, modulates the MT diameter providing insight for the control of geometric parameters in bio- nanotechnology. In another set of experiments we describe lipid-protein- nanotubes, and lipid nano- tubes and rods, resulting from membrane shape evolution processes involving protein templates and curvature stabilizing lipids. Similar membrane shape changes, occurring in cells for the purpose of specific functions, are induced by interactions between membranes and proteins. The biological materials systems described have applications in bio-nanotechnology. Supramolecular structures of bundles and loop-like networks of microtubules in the presence of counterions (blue/red spheres comprise the tubule wall), and nanorods and nanotubes of block liposomes comprised of charged curvature-stabilizing-lipids (green/yellow), determined by synchrotron X-ray scattering and electron microscopy including cryogenic TEM. The distinct microtubule bundles and lipid nanotubes and nanorods have applications in nanotechnology and biotechnology.