Kinetic measurements of protein conformation in a microchip

Refolding techniques for recovering biologically active recombinant proteins from inclusion bodies

Biologically active proteins are useful for studying the biological functions of genes and for the development of therapeutic drugs and biomaterials in a biotechnology industry. Overexpression of recombinant proteins in bacteria, such as Escherichia coli, often results in the formation of inclusion bodies, which are protein aggregates with non-native conformations. As inclusion bodies contain relatively pure and intact proteins, protein refolding is an important process to obtain active recombinant proteins from inclusion bodies. However, conventional refolding methods, such as dialysis and dilution, are time consuming and, often, recovered yields of active proteins are low, and a trial-and-error process is required to achieve success. Recently, several approaches have been reported to refold these aggregated proteins into an active form. The strategies largely aim at reducing protein aggregation during the refolding procedure. This review focuses on protein refolding techniques using chemical additives and laminar flow in microfluidic chips for the efficient recovery of active proteins from inclusion bodies.

A microfluidic device for bacteria detection in aqueous samples

We demonstrate the use of a microfluidic device that accurately monitors bacteria levels in water. Fluorescent antibody labelled E. coli K12 bacteria in aqueous samples are flowed through the device, and spikes in the emission signal correspond to the presence of bacteria. Target bacteria could also be detected while suspended in a suspension of very low antibody concentration, suggesting that washing of bacteria could be avoided to make the detection automated and more rapid. Use of a microfluidic device will eventually enable quick on-site detection of bacteria using small quantities of sample.

Protein denaturation and protein:drugs interactions from intrinsic protein fluorescence measurements at the nanolitre scale

Protein stability and ligand-binding affinity measurements are widely required for the formulation of biopharmaceutical proteins, protein engineering and drug screening within life science research. Current techniques either consume too much of often precious biological or compound materials, in large sample volumes, or alternatively require chemical labeling with fluorescent tags to achieve measurements at submicrolitre volumes with less sample. Here we present a quantitative and accurate method for the determination of protein stability and the affinity for small molecules, at only 1.5-20 nL optical sample volumes without the need for fluorescent labeling, and that takes advantage of the intrinsic tryptophan fluorescence of most proteins. Coupled to appropriate microfluidic sample preparation methods, the sample requirements could thus be reduced 85,000-fold to just 10(8) molecules. The stability of wild-type FKBP-12 and a destabilizing binding-pocket mutant are studied in the presence and absence of rapamycin, to demonstrate the potential of the technique to both drug screening and protein engineering. The results show that 75% of the interaction energy between FKBP-12 and rapamycin originates from residue Phe99 in the binding site.

A microfluidic mixing system for single-molecule measurements

This article describes the design and fabrication of a microfluidic mixing system optimized for ultrasensitive optical measurements. Channels are replica-molded in polydimethylsiloxane elastomer and sealed with fused-silica coverglass. The resulting devices have broad chemical compatibility and extremely low fluorescence background, enabling measurements of individual molecules under well-characterized nonequilibrium conditions. Fluid delivery and pressure connections are made using an interface that allows for rapid assembly, rapid sample exchange, and modular device replacement while providing access for high numerical aperture optics.

Evaluation of continuous flow nanosphere formation by controlled microfluidic transport

Improved size monodispersity of populations of polymer nanospheres is of enormous interest in the fields of nanotechnology and nanomedicine. As such, the knowledge of exact experimental conditions for precise production of nanospheres is needed for nonaqueous systems. This work presents the use of controlled microfluidic transport methods to study the experimental parameters for fabricating nanoparticles utilizing phase inversion. We report two microfluidic methods for forming polymer nanospheres in small batches to determine the formation conditions. These conditions were then implemented to perform higher throughput formation of polymer nanospheres of the desired size. The controlled microfluidic environment in the laminar flow regime produces improved size monodispersity, decreased average diameter, and affords a greater degree of control over the nanosphere size distribution without adding surfactants or additional solvents. Experiments show a nonlinear trend toward decreasing size with decreasing polymer concentration and a linear trend toward decreasing size with increasing flow rate indicating time-course-dependent nucleation and growth mechanism of formation for the resultant nanosphere population within the range of conditions tested.

Extrinsic fluorescent dyes as tools for protein characterization

Noncovalent, extrinsic fluorescent dyes are applied in various fields of protein analysis, e.g. to characterize folding intermediates, measure surface hydrophobicity, and detect aggregation or fibrillation. The main underlying mechanisms, which explain the fluorescence properties of many extrinsic dyes, are solvent relaxation processes and (twisted) intramolecular charge transfer reactions, which are affected by the environment and by interactions of the dyes with proteins. In recent time, the use of extrinsic fluorescent dyes such as ANS, Bis-ANS, Nile Red, Thioflavin T and others has increased, because of their versatility, sensitivity and suitability for high-throughput screening. The intention of this review is to give an overview of available extrinsic dyes, explain their spectral properties, and show illustrative examples of their various applications in protein characterization.