Effect of Liposome Size on Internal RNA Replication Coupled with Replicase Translation.

Cell membranes inhibit the diffusion of intracellular materials, and compartment size can strongly affect the intracellular biochemical reactions. To assess the effect of the size of microcompartments on intracellular reactions, we constructed a primitive cell model consisting of giant liposomes and a translation-coupled RNA replication (TcRR) system. The RNA was replicated by Qß replicase, which was translated from the RNA in giant liposomes encapsulating the cell-free translation system. A reporter RNA encoding the antisense strand of ß-glucuronidase was introduced into the system to yield a TcRR read-out (green fluorescence). We demonstrate that TcRR was hardly detectable in larger liposomes (230 fL) but was more effective in smaller (7.7 fL) liposomes. Our experimental and theoretical results show that smaller microcompartments considerably enhance TcRR because the synthesized molecules, such as RNA and replicases, are more concentrated in smaller liposomes.

Construction of a gene screening system using giant unilamellar liposomes and a fluorescence-activated cell sorter.

We have constructed a gene screening system composed of an in vitro transcription-translation system encapsulated within giant unilamellar liposomes and a fluorescence-activated cell sorter (FACS), which allows high-throughput screening of genes encoding proteins of interest. A mock gene library of ß-glucuronidase (GUS) was compartmentalized into liposomes at the single-molecule level, and liposomes exhibiting green fluorescence derived from hydrolysis of the fluorogenic substrate by the synthesized enzyme were sorted using FACS. More than 10-fold enrichment of GUS gene with higher catalytic activity was obtained when a single copy of the GUS gene was encapsulated in each liposome. Quantitative analysis of the enrichment factors and their liposome size dependencies showed that experimentally obtained and theoretical values were in agreement. Using this method, genes encoding active GUS were then enriched from a gene library of randomly mutated GUS genes. Only three rounds of screening were required, which was also consistent with our theoretical estimation.

Nitric oxide release in human aortic endothelial cells mediated by delivery of amphiphilic polysiloxane nanoparticles to caveolae.

Microdomains such as lipid raft and caveolae are organized as functional compartments in plasma membrane of cells. In this study, we note the functional platform of caveolae with dual functions, internalization of external substances and cell signalings leading to nitric oxide release, and hypothesize that the switching of enzyme activity of endothelial nitric oxide synthase can be achieved by targeting caveolae with nanoparticles. We prepared polysiloxane nanoparticles and studied cellular uptake of the nanoparticles and its concomitant influence on the nitric oxide release in human aortic endothelial cells. We found that polysiloxane nanoparticles were endocytosed via caveolae in human aortic endothelial cells and that enhanced nitric oxide release was followed by the cellular uptake of the nanoparticles. Furthermore, we confirmed that endothelial nitric oxide synthase was activated during cellular uptake of the nanoparticles. These findings support our idea that delivery of the polymeric nanoparticles to endothelial cells can lead to the induction of nitric oxide release.

Substrata mechanical stiffness can regulate adhesion of viable bacteria.

The competing mechanisms that regulate adhesion of bacteria to surfaces and subsequent biofilm formation remain unclear, though nearly all studies have focused on the role of physical and chemical properties of the material surface. Given the large monetary and health costs of medical-device colonization and hospital-acquired infections due to bacteria, there is considerable interest in better understanding of material properties that can limit bacterial adhesion and viability. Here we employ weak polyelectrolyte multilayer (PEM) thin films comprised of poly(allylamine) hydrochloride (PAH) and poly(acrylic acid) (PAA), assembled over a range of conditions, to explore the physicochemical and mechanical characteristics of material surfaces controlling adhesion of Staphylococcus epidermidis bacteria and subsequent colony growth. Although it is increasingly appreciated that eukaryotic cells possess subcellular structures and biomolecular pathways to sense and respond to local chemomechanical environments, much less is known about mechanoselective adhesion of prokaryotes such as these bacteria. We find that adhesion of viable S. epidermidis correlates positively with the stiffness of these polymeric substrata, independently of the roughness, interaction energy, and charge density of these materials. Quantitatively similar trends observed for wild-type and actin analogue mutant Escherichia coli suggest that these results are not confined to only specific bacterial strains, shapes, or cell envelope types. These results indicate the plausibility of mechanoselective adhesion mechanisms in prokaryotes and suggest that mechanical stiffness of substrata materials represents an additional parameter that can regulate adhesion of and subsequent colonization by viable bacteria.

Amphiphilic poly(N-propargylamide) with galactose and lauryloyl groups: synthesis and properties.

An amphiphilic poly(N-propargylamide) with galactose and lauryloyl groups was synthesized by copolymerization of the corresponding N-propargylamide monomers using a Rh catalyst. The obtained copolymer formed a one-handed helical conformation and molecular aggregates in water. The observations by fluorescence microscopy in a cell culture experiment in the presence of dye-labeled copolymer indicated that the copolymer was incorporated into the cells.

Liposome display for in vitro selection and evolution of membrane proteins.

Liposome display is a novel method for in vitro selection and directed evolution of membrane proteins. In this approach, membrane proteins of interest are displayed on liposome membranes through translation from a single DNA molecule by using an encapsulated cell-free translation system. The liposomes are probed with a fluorescence indicator that senses membrane protein activity and selected using a fluorescence-activated cell sorting (FACS) instrument. Consequently, DNA encoding a protein with a desired function can be obtained. By implementing this protocol, researchers can process a DNA library of 10(7) different mutants. A single round of the selection procedure requires 24 h for completion, and multiple iterations of this technique, which take 1-5 weeks, enable the isolation of a desired gene. As this protocol is conducted entirely in vitro, it enables the engineering of various proteins, including pore-forming proteins, transporters and receptors. As a useful example of the approach, here we detail a procedure for the in vitro evolution of α-hemolysin from Staphylococcus aureus for its pore-forming activity.

Directed Evolution of Proteins through In Vitro Protein Synthesis in Liposomes.

Directed evolution of proteins is a technique used to modify protein functions through "Darwinian selection." In vitro compartmentalization (IVC) is an in vitro gene screening system for directed evolution of proteins. IVC establishes the link between genetic information (genotype) and the protein translated from the information (phenotype), which is essential for all directed evolution methods, by encapsulating both in a nonliving microcompartment. Herein, we introduce a new liposome-based IVC system consisting of a liposome, the protein synthesis using recombinant elements (PURE) system and a fluorescence-activated cell sorter (FACS) used as a microcompartment, in vitro protein synthesis system, and high-throughput screen, respectively. Liposome-based IVC is characterized by in vitro protein synthesis from a single copy of a gene in a cell-sized unilamellar liposome and quantitative functional evaluation of the synthesized proteins. Examples of liposome-based IVC for screening proteins such as GFP and ß-glucuronidase are described. We discuss the future directions for this method and its applications.