In an effort to favor the formation of straight polymer chains without crystalline grain boundaries, we have synthesized an amphiphilic conjugated polyelectrolyte, poly(fluorene-alt-thiophene) (PFT), which self-assembles in aqueous solutions to form cylindrical micelles. In contrast to many diblock copolymer assemblies, the semiconducting backbone runs parallel, not perpendicular, to the long axis of the cylindrical micelle. Solution-phase micelle formation is observed by X-ray and visible light scattering. The micelles can be cast as thin films, and the cylindrical morphology is preserved in the solid state. The effects of self-assembly are also observed through spectral shifts in optical absorption and photoluminescence. Solutions of higher-molecular-weight PFT micelles form gel networks at sufficiently high aqueous concentrations. Rheological characterization of the PFT gels reveals solid-like behavior and strain hardening below the yield point, properties similar to those found in entangled gels formed from surfactant-based micelles. Finally, electrical measurements on diode test structures indicate that, despite a complete lack of crystallinity in these self-assembled polymers, they effectively conduct electricity.

The inside surfaces of the protein shells of many viruses are positively charged, thereby enhancing the self-assembly of capsid proteins around their (oppositely charged) RNA genome. These proteins have been shown to organize similarly around a variety of nonbiological, negatively charged, polymers, for example, poly(styrene sulfonate) (PSS), forming virus-like particles (VLPs). We have demonstrated recently that the VLPs formed from cowpea chlorotic mottle virus (CCMV) capsid protein increase in size (from T=2 to T=3 structures) upon increase in PSS molecular weight (from 400 kDa to 3.4 MDa), and that the total charge on the PSS exceeds that of the capsid protein by as much as a factor of 9. Here, we extend studies of this kind to PSS molecules that are sufficiently small that two or more can be packaged into VLPs. The use of 38 kDa PSS polymers that have been fluorescently labeled with Rhodamine B allows us to determine the number of PSS molecules per capsid. Electron micrographs of the VLPs show a bimodal distribution of particle diameters, with one peak centered around 19 nm, typical of a T=1 triangulation number, and the other around 21 nm, consistent with a pseudo T=2 structure; increasing the molar ratio of protein to PSS in the reaction mix shifts the VLP distribution from T=1 to T=2 structures. By combining fluorescence and gel electrophoresis measurements, it is determined that, on average, there are two polymers in each T=1 capsid and three in each T=2, with the PSS charge less than that of the capsid protein by as much as a factor of 2. VLPs of this kind provide a versatile model system for determining the principles underlying self-assembly of controlled numbers of cargo molecules in nanocontainers of increasing size.

Cowpea chlorotic mottle virus is a single-stranded RNA plant virus with a diameter of 28 nm. The proteins comprising the capsid of this virus can be purified and reassembled either by themselves to form hollow structures or with polyanions such as double-stranded DNA or single-stranded RNA. Depending on pH and ionic strength, a diverse range of structures and shapes can form. The work presented here focuses on using these proteins to encapsulate a fluorescent polyanionic semiconducting polymer, MPS-PPV (poly-2-methoxy-5-propyloxy sulfonate phenylene vinlyene), in order to obtain optically active virus-like particles. After encapsulation, fluorescence from MPS-PPV shows two distinct peaks, which suggests the polymer may be in two conformations. A combination of TEM, fluorescence anisotropy, and sucrose gradient separation indicate that the blue peak arises from polymer encapsulated into spherical particles, while the redder peak corresponds to polymers contained in rod-like cages. Ionic strength during assembly can be used to tune the propensity to form rods or spheres. The results illustrate the synergy of hybrid synthetic/biological systems: polymer conformation drives the structure of this composite material, which in turn modifies the polymer optical properties. This synergy could be useful for the future development of synthetic/biological hybrid materials with designated functionality.

Vaults are naturally occurring ribonucleoprotein particles with an enormous interior volume, large enough to encapsulate hundreds of proteins. They are highly conserved and are present in nearly all eukaryotic cells ranging from 10(4) to 10(7) particles per cell. Recombinant vaults can be produced In vitro and engineered to allow cell targeting and protein packaging. These nanometer-sized particles have many desirable characteristics that may give them advantages for use as drug delivery vehicles. Using photoactivatable green fluorescent protein (PAGFP) labeled vaults, we demonstrate that the particles rapidly diffuse throughout the cytoplasm following single pixel photoactivation in live cells. Their in vivo movement remained relatively unchanged despite exposure to a variety of cellular stresses, suggesting that vaults are largely unconstrained in the cytoplasm. Fluorescence resonance energy transfer (FRET) was observed from polyethylene glycol (PEG) fused hybrid cells that expressed either CFP or YFP labeled vaults, indicating that vaults can exchange major vault protein (MVP) subunits in vivo. Investigation into the mechanism of this exchange in vitro using recombinant vaults demonstrated that they were capable of rapidly separating at the particle waist and reassembling back into whole vaults, supporting a half vault exchange mechanism. This data suggests a means whereby vaults can functionally interact with their cellular environment and deliver materials packaged within their interior.

We demonstrate that a semiconducting polymer [poly(2-methoxy-5-propyloxy sulfonate phenylene vinylene), MPS-PPV] can be encapsulated inside recombinant, self-assembling protein nanocapsules called "vaults". Polymer incorporation into these nanosized protein cages, found naturally at approximately 10,000 copies per human cell, was confirmed by fluorescence spectroscopy and small-angle X-ray scattering. Although vault cellular functions and gating mechanisms remain unknown, their large internal volume and natural prevalence within the human body suggests they could be used as carriers for therapeutics and medical imaging reagents. This study provides the groundwork for the use of vaults in encapsulation and delivery applications.

Vaults are ubiquitous, self-assembled protein nanocapsules with dimension in the sub-100 nm range that are conserved across diverse phyla from worms to humans. Their normal presence in humans at a copy number of over 10 000/cell makes them attractive as potential drug delivery vehicles. Toward this goal, bifunctional amine-reactive reagents are shown to be useful for the reversible cross-linking of recombinant vaults such that they may be closed and opened in a controllable manner.