Precise and comparative pegylation analysis by microfluidics and mass spectrometry

NAD(H)-PEG Swing Arms Improve Both the Activities and Stabilities of Modularly-Assembled Transhydrogenases Designed with Predictable Selectivities

Protein engineering has been used to enhance the activities, selectivities, and stabilities of enzymes.  Frequently tradeoffs are observed, where improvements in some features can come at the expense of others.  Nature uses modular assembly of active sites for complex, multi-step reactions, and natural "swing arm" mechanisms have evolved to transfer intermediates between active sites.  Biomimetic polyethylene glycol (PEG) swing arms modified with NAD(H) have been explored to introduce synthetic swing arms into fused oxidoreductases.  Here we report that increasing NAD(H)-PEG swing arms can improve the activity of synthetic formate:malate oxidoreductases as well as the thermal and operational stabilities of the biocatalysts.  The modular assembly approach enables the K M values of new enzymes to be predictable, based on the parental enzymes.  We describe four unique synthetic transhydrogenases that have no native homologs, and this platform could be easily extended for the predictive design of additional synthetic cofactor-independent transhydrogenases.

Continuous flow microreactor for protein PEGylation

PEGylation is increasingly being utilized to enhance the therapeutic efficacy of biopharmaceuticals. Various chemistries and reaction conditions have been established to synthesize PEGylated proteins and more are being developed. Both the extent of conversion and selectivity of protein PEGylation are highly sensitive to process variables and parameters. Therefore, microfluidic-based high-throughput screening platforms would be highly suitable for optimization of protein PEGylation. As part of this study, a poly-dimethylsiloxane-based continuous flow microreactor system was designed and its performance was compared head-to-head with a batch reactor. The reactants within the microreactor were contacted by passive micromixing based on chaotic advection generated by staggered herringbone grooves embedded in serpentine microchannels. The microreactor system was provided with means for on-chip reaction quenching. Lysozyme was used as the model protein while methoxy-polyethylene glycol-(CH2)5COO-NHS was used as the PEGylation reagent. Full mixing was achieved close to the microreactor inlet, making the device suitable for protein PEGylation. The effect of mixing type, i.e., simple stirring versus chaotic laminar mixing on PEGylation, was investigated. Higher selectivity (as high as 100% selectivity) was obtained with the microreactor while the conversion was marginally lower.

Lanthanide-based upconversion nanoparticles for connexin-targeted imaging in co-cultures

From the perspective of deep tissue imaging, it is required that the excitation light can penetrate deep enough to excite the sample of interest and the fluorescence emission is strong enough to be detected. The longer wavelengths like near infrared are absorbed less by the tissue and are scattered less implying deeper penetration. This has drawn interest to the class of nanoparticles called upconversion nanoparticles (UCNs) which has an excitation in the near-infrared wavelength and the emission is in the visible/near-infrared wavelength (depending on the doped ions). Here, we discuss surface modification of the UCNs to make them hydrophilic allowing dispersion in physiological buffers and enabling conjugation of antibody to their surface. It was of interest to use connexin 43 gap junction protein-specific antibody on UCNs to target cardiac cell such as H9c2 and co-culture of bone marrow stem cells and H9c2.

Rapid detection and quantification of specific proteins by immunodepletion and microfluidic separation

Conventional immunoblotting techniques are labor intensive, time consuming and rely on the elution of target protein after depletion. Here we describe a new method for detection and quantification of proteins, independent of washing and elution. In this method, the target protein is first captured by immunodepletion with antibody-coated microbeads. In the second step, both the supernatant after immunodepletion and the untreated protein sample are directly analyzed by microfluidic electrophoresis without further processing. Subsequently, the detection and quantification are performed by comparing the electropherograms of these two samples. This method was tested using an Escherichia coli lysate with a FLAG-tagged protein and anti-FLAG magnetic beads. An incubation of as short as one min was sufficient for detectable depletion (66%) by microchip electrophoresis. Longer incubation (up to 60 min) resulted in more depletion of the target band (82%). Our results show that only 19% of the target is recovered after elution from the beads. By eliminating multiple wash and elution steps, our method is faster, less labor intensive, and highly reproducible. The target protein can still be easily identified even in the case of nonspecific binding at low concentrations. This work highlights the advantages of integrating immunodepletion techniques on a microfluidic platform.

MALDI linear TOF mass spectrometry of PEGylated (glyco)proteins

PEGylation of proteins is a fast growing field in biotechnology and pharmaceutical sciences owing to its ability to prolong the serum half-life time of recombinant proteins. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) has been shown to be a powerful tool in the analysis of several PEGylated small proteins. Here we present data obtained with a standard secondary electron multiplier (SEM) and a high mass (HM) detector combined with a MALDI linear TOF MS system for the detection of PEGylated (glyco)proteins in the range of 60-600 kDa. Examples of MALDI TOF MS of small (interferon alpha2a), middle (human serum albumin (HSA)) and high molecular mass proteins (coagulation factor VIII and von Willebrand factor (vWF), both heavily glycosylated proteins) are presented. The particular challenge for the analysis was the heterogeneity of the (glyco)proteins in the high molecular weight range in combination with additional PEGylation, which even introduced more heterogeneity and was more challenging for interpretation. Nevertheless, the performance of MALDI linear TOF MS with both detector systems in terms molecular weight and heterogeneity determination depending on the m/z range was superior to the other methods. Although the SEM was able to obtain information about protein PEGylation in the mass range up to 100 kDa (e.g. PEGylated HSA), the HM system was crucial for detection of HM ions (e.g. PEGylated recombinant vWF), which was impossible with the standard SEM.

Microchip CGE linked to immunoprecipitation as an alternative to Western blotting

A novel approach for protein identification is presented, which combines the specificity of an immunoprecipitation approach with the sensitivity of protein detection in microchip CGE. This method involves derivatization of the sample proteins with a fluorescent dye, target protein isolation with specific antibodies and Protein A coated magnetic beads, and automated sizing and quantification of the eluted samples on microchips. The performance of the new technique was demonstrated with glutathion-S-transferase- and polyHistidine-tagged target proteins in an Escherichia coli background. A specific detection of target proteins was possible down to 0.001% or 1 ng target protein in a background of 100 microg E. coli protein. With this approach, proteins ranging from 10 to 220 kDa could be identified with a panel of different target-specific antibodies. The reproducibility of the method was very similar to standard microchip CGE methods. In a direct comparison to Western blotting, a similar sensitivity and specificity of both techniques was observed. However, the new approach compares favorably to Western blotting in terms of time-to-result, usability and labor intensity, antibody consumption and access to quantitative data.