Site-Specific Labeling of Surface Proteins on Living Cells Using Genetically Encoded Peptides that Bind Fluorescent Nanoparticle Probes

Self-suspended suspensions of covalently grafted hairy nanoparticles

Dispersions of small particles in liquids have been studied continuously for almost two centuries for their ability to simultaneously advance understanding of physical properties of fluids and their widespread use in applications. In both settings, the suspending (liquid) and suspended (solid) phases are normally distinct and uncoupled on long length and time scales. In this study, we report on the synthesis and physical properties of a novel family of covalently grafted nanoparticles that exist as self-suspended suspensions with high particle loadings. In such suspensions, we find that the grafted polymer chains exhibit unusual multiscale structural transitions and enhanced conformational stability on subnanometer and nanometer length scales. On mesoscopic length scales, the suspensions display exceptional homogeneity and colloidal stability. We attribute this feature to steric repulsions between grafted chains and the space-filling constraint on the tethered chains in the single-component self-suspended materials, which inhibits phase segregation. On macroscopic length scales, the suspensions exist as neat fluids that exhibit soft glassy rheology and, counterintuitively, enhanced elasticity with increasing temperature. This feature is discussed in terms of increased interpenetration of the grafted chains and jamming of the nanoparticles.

Dye-doped silica nanoparticles as luminescent organized systems for nanomedicine

This review summarizes developments and applications of luminescent dye doped silica nanoparticles as versatile organized systems for nanomedicine.

Modeling Pressure-Driven Transport of Proteins through a Nanochannel

Reducing the size of a nanofluidic channel not only creates new opportunities for high-precision manipulation of biological macromolecules, but also makes the performance of the entire nanofluidic system more susceptible to undesirable interactions between the transported biomolecules and the walls of the channel. In this manuscript, we report molecular dynamics simulations of a pressure-driven flow through a silica nanochannel that characterized, with atomic resolution, adsorption of a model protein to its surface. Although the simulated adsorption of the proteins was found to be nonspecific, it had a dramatic effect on the rate of the protein transport. To determine the relative strength of the protein-silica interactions in different adsorbed states, we simulated flow-induced desorption of the proteins from the silica surface. Our analysis of the protein conformations in the adsorbed states did not reveal any simple dependence of the adsorption strength on the size and composition of the protein-silica contact, suggesting that the heterogeneity of the silica surface may be a important factor.

Production of secretory and extracellular N-linked glycoproteins in Escherichia coli

The Campylobacter jejuni pgl gene cluster encodes a complete N-linked protein glycosylation pathway that can be functionally transferred into Escherichia coli. In this system, we analyzed the interplay between N-linked glycosylation, membrane translocation and folding of acceptor proteins in bacteria. We developed a recombinant N-glycan acceptor peptide tag that permits N-linked glycosylation of diverse recombinant proteins expressed in the periplasm of glycosylation-competent E. coli cells. With this "glycosylation tag," a clear difference was observed in the glycosylation patterns found on periplasmic proteins depending on their mode of inner membrane translocation (i.e., Sec, signal recognition particle [SRP], or twin-arginine translocation [Tat] export), indicating that the mode of protein export can influence N-glycosylation efficiency. We also established that engineered substrate proteins targeted to environments beyond the periplasm, such as the outer membrane, the membrane vesicles, and the extracellular medium, could serve as substrates for N-linked glycosylation. Taken together, our results demonstrate that the C. jejuni N-glycosylation machinery is compatible with distinct secretory mechanisms in E. coli, effectively expanding the N-linked glycome of recombinant E. coli. Moreover, this simple glycosylation tag strategy expands the glycoengineering toolbox and opens the door to bacterial synthesis of a wide array of recombinant glycoprotein conjugates.