Conformations and membrane-driven self-organization of rodlike fd virus particles on freestanding lipid membranes

Membrane-mediated interactions of macromolecules and colloids bound to elastic responsive lipid membranes have garnered much attention owing to the fact that represent an exciting challenge in soft matter physics with relevance to biology and molecular pharmacology. Elucidating the mechanisms of interactions of nanomaterials with lipid membranes is essential in development of numerous applications including drug delivery, gene therapy, in vitro and in vivo bio-imaging, as well as for better understanding the biological mechanisms at the molecular level.

Based on the existing theoretical and simulation-based studies, it has already been established that local deformations of elastic membranes induced by the binding of colloids can result in attractive interactions capable of driving their clustering and self-organization. Up to now, however, experiments addressed only the behavior of spherical membrane-bound colloids. On the other hand, rodlike colloidal particles have been predicted to show membrane-driven self-organization controlled by the tension and curvature of the underlying membrane, which is believed to be relevant for understanding the biologically vital issues of membrane budding and tubulation. So far, the aspects of such membrane-mediated interactions of rodlike colloids have not been investigated experimentally.

Researchers led by Dr. Eugene P. Petrov from the Max Planck Institute of Biochemistry in Germany experimentally addressed the effects of the interaction of semiflexible colloidal rods with a responsive elastic membrane. They did it by studying the behavior of filamentous virus fd electrostatically bound to freestanding cationic lipid bilayers and lipid nanotubes. Their work is published in the research journal, Soft Matter.

The research team used fd virus which is known to be a good model system of rodlike colloidal particles. Bacteriophage fd that infects E. coli is a good model system to study liquid crystalline behavior because it is easily grown in large quantities, monodisperse and stable in solution. Furthermore, fd virus is widely employed in cloning, phage display, nanotechnology, biosensing, and biomedicine.

The researchers employed single-particle fluorescence video-microscopy to study the interaction of rodlike semiflexible fd virus particles with freestanding cationic lipid membranes. In the process, they varied the membrane charge and ionic strength of the surrounding medium, which in turn allowed them to distinguish amongst the three diverse regimes the behavior of membrane-adsorbed fd virus particles.

The authors observed that the weakly charged freestanding cationic lipid bilayer in low-ionic strength medium represented a gentle quasi-2D substrate thereby preserving the integrity, structure and mechanical properties of fd virus particles. Secondly, they noted that upon increase of the membrane charge, the filamentous virus particles underwent membrane-driven collapse and formed sub-micrometer-sized globules that remained attached to the bilayer or lipid nanotubes. Thirdly, the team realized that when the membrane charge was low and a non-negligible ionic strength screening medium was used, the membrane-driven self-organization of membrane-bound fd virus particles resulted in formation of linear tip-to-tip aggregates.

The study presented an experimental demonstration of the behavior of rodlike colloidal particles adsorbed on responsive elastic membranes that can be controlled by membrane-mediated interactions.

The Max Planck Institute of Biochemistry researchers study can serve as a springboard for future experimental and simulation efforts aimed at elucidation of biological mechanisms as well as deeper understanding the physics of the interactions of colloids and polymers with elastic lipid membrane.