Fabrication of an on-line enzyme micro-reactor coupled to liquid chromatography–tandem mass spectrometry for the digestion of recombinant human erythropoietin

Development of automated proteomic workflows utilizing silicon-based coupling agents

Automated methods for enzyme immobilization via 4-triethoxysilylbutyraldehyde (TESB) derived silicone-based coupling agents were developed. TESB and its oxidized derivative, 4-triethoxysilylbutanoic acid (TESBA), were determined to be the most effective. The resulting immobilized enzyme particles (IEPs) displayed robustness, rapid digestion, and immobilization efficiency of 51 ± 8%. Furthermore, we automated the IEP procedure, allowing for multiple enzymes, and/or coupling agents to be fabricated at once, in a fraction of the time via an Agilent Bravo. The automated trypsin TESB and TESBA IEPs were shown to rival a classical in-gel digestion method. Moreover, pepsin IEPs favored cleavage at leucine (>50%) over aromatic and methionine residues. The IEP method was then adapted for an in-situ immobilized enzyme microreactor (IMER) fabrication. We determined that TESBA could functionalize the silica capillary's inner wall while simultaneously acting as an enzyme coupler. The IMER digestion of bovine serum albumin (BSA), mirroring IEP digestion conditions, yielded a 33-40% primary sequence coverage per LC-MS/MS analysis in as little as 15 min. Overall, our findings underscore the potential of both IEP and IMER methods, paving the way for automated analysis and a reduction in enzyme waste through reuse, thereby contributing to a more cost-effective and timely study of the proteome. SIGNIFICANCE: This research introduces 4-triethoxysilylbutyraldehyde (TESB) and its derivatives as silicon-based enzyme coupling agents and an automated liquid handling method for bottom-up proteomics (BUP) while streamlining sample preparation for high-throughput processing. Additionally, immobilized enzyme particle (IEP) fabrication and digestion within the 96-well plate allows for flexibility in protocol where different enzyme-coupler combinations can be employed simultaneously. By enabling the digestion of entire microplates and reducing manual labor, the proposed method enhances reproducibility and offers a more efficient alternative to classical in-gel techniques. Furthermore, pepsin IEPs were noted to favor cleavage at leucine residues which represents an interesting finding when compared to the literature that warrants further study. The capability of immobilized enzyme microreactors (IMER) for rapid digestion (in as little as 15 min) demonstrated the system's efficiency and potential for rapid proteomic analysis. This advancement in BUP not only improves efficiency, but also opens avenues for a fully automated, mass spectrometry-integrated proteomics workflow, promising to expedite research and discoveries in complex biological studies.

Application of Spectroscopy Techniques for Monitoring (Bio)Catalytic Processes in Continuously Operated Microreactor Systems

In the last twenty years, the application of microreactors in chemical and biochemical industrial processes has increased significantly. The use of microreactor systems ensures efficient process intensification due to the excellent heat and mass transfer within the microchannels. Monitoring the concentrations in the microchannels is critical for a better understanding of the physical and chemical processes occurring in micromixers and microreactors. Therefore, there is a growing interest in performing in-line and on-line analyses of chemical and/or biochemical processes. This creates tremendous opportunities for the incorporation of spectroscopic detection techniques into production and processing lines in various industries. In this work, an overview of current applications of ultraviolet–visible, infrared, Raman spectroscopy, NMR, MALDI-TOF-MS, and ESI-MS for monitoring (bio)catalytic processes in continuously operated microreactor systems is presented. The manuscript includes a description of the advantages and disadvantages of the analytical methods listed, with particular emphasis on the chemometric methods used for spectroscopic data analysis.

Design, Heterologous Expression, and Application of an Immobilized Protein Kinase

Protein kinase A (PKA) is a biologically important enzyme for cell regulation, often referred to as the "central kinase". An immobilized PKA that retains substrate specificity and activity would be a useful tool for laboratory scientists, enabling targeted phosphorylation without interference from downstream kinase contamination or kinase autophosphorylation in sensitive assays. Moreover, it might also provide the benefits of robustness and reusability that are often associated with immobilized enzyme preparations. In this work, we describe the creation of a recombinant PKA fusion protein that incorporates the HaloTag covalent immobilization system. We demonstrate that protein fusion design, including affinity tag placement, is critical for optimal heterologous expression in Escherichia coli. Furthermore, we demonstrate various applications of our immobilized PKA, including the phosphorylation of recombinant PKA substrates, such as vasodilator-stimulated phosphoprotein, and endogenous PKA substrates in a cell lysate. This immobilized PKA also possesses robust activity and reusability over multiple trials. This work holds promise as a generalizable strategy for the production and application of immobilized protein kinases.

Monitoring of phosphorylation using immobilized kinases by on-line enzyme bioreactors hyphenated with High-Resolution Mass Spectrometry

Nucleosides analogues are the cornerstone of the treatment of several human diseases. They are especially at the forefront of antiviral therapy. Their therapeutic efficiency depends on their capacity to be converted to the active nucleoside triphosphate form through successive phosphorylation steps catalyzed by nucleoside/nucleotide kinases. In this context, it is mandatory to develop a rapid, reliable and sensitive enzyme activity test to evaluate their metabolic pathways. In this study, we report a proof of concept to directly monitor on-line nucleotide multiple phosphorylation. The methodology was developed by on-line enzyme bioreactors hyphenated with High-Resolution Mass Spectrometry detection. Human Thymidylate Kinase (hTMPK) and human Nucleoside Diphosphate Kinase (hNDPK) were covalently immobilized on functionalized silica beads, and packed into micro-bioreactors (40 μL). By continuous infusion of substrate into the bioreactors, the conversion of thymidine monophosphate (dTMP) into its di- (dTDP) and tri-phosphorylated (dTTP) forms was visualized by monitoring their Extracted Ion Chromatogram (EIC) of their [M - H]^- ions. Both bioreactors were found to be robust and durable over 60 days (storage at 4 °C in ammonium acetate buffer), after 20 uses and more than 750 min of reaction, making them suitable for routine analysis. Each on-line conversion step was shown rapid (<5 min), efficient (conversion efficiency > 55%), precise and repeatable (CV < 3% for run-to-run analysis). The feasibility of the on-line multi-step conversion from dTMP to dTTP was also proved. In the context of selective antiviral therapy, this proof of concept was then applied to the monitoring of specificity of conversion of two synthesized Acyclic Nucleosides Phosphonates (ANPs), regarding human Thymidylate Kinase (hTMPK) and vaccina virus Thymidylate Kinase (vvTMPK).

Novel approaches for biomolecule immobilization in microscale systems

This manuscript reviews novel approaches applied for biomolecule immobilization in microscale systems.

Multienzyme Cascade Bioreactor for a 10 min Digestion of Genomic DNA into Single Nucleosides and Quantitative Detection of Structural DNA Modifications in Cellular Genomic DNA

Identification and quantification of chemical DNA modifications provide essential information on genomic DNA changes, for example, epigenetic modifications and abnormal DNA lesions. In this vein, it requires to digest genomic DNA strands into single nucleosides, facilitating the mass spectrometry analysis. However, rapid digestion of such supramacromolecule DNA of several millions Daltons (molecular weight) into single nucleosides remains very challenging. Here, we constructed an immobilized benzonase capillary bioreactor and further tandemly coupled with immobilized snake venom phosphodiesterase and alkaline phosphatase capillary bioreactor to form a novel three-enzyme cascade bioreactor (BenzoSAC bioreactor). In these constructions, the chosen enzymes were immobilized onto synthetic porous capillary silica monoliths. With the tailor-made porous structure and high immobilized capacity and high digestion rate of benzonase, genomic DNA of >99.5% can be digested into single nucleosides within only 10 min when passing through the BenzoSAC bioreactor by microinjection pump. In contrast, traditional digestion requires 8-24 h. By offline coupling this benzoSAC bioreactor with liquid chromatography-tandem mass spectrometry, we detected 5-hydroxymethylcytosine, a major oxidation product of the epigenetically crucial 5-methylcytosine, in genomic DNA isolated from ladder cancer (T24) cells. The newly synthesized BenzoSAC bioreactor and the proposed mass spectrometry detection are promising for fast identification and analysis of structural modifications in DNA.

Multichannel Open Tubular Enzyme Reactor Online Coupled with Mass Spectrometry for Detecting Ricin

For counterterrorism purposes, a selective nano liquid chromatography-mass spectrometry (nanoLC-MS) platform was developed for detecting the highly lethal protein ricin from castor bean extract. Manual sample preparation steps were omitted by implementing a trypsin/Lys-C enzyme-immobilized multichannel reactor (MCR) consisting of 126 channels (8 μm inner diameter in all channels) that performed online digestion of proteins (5 min reaction time, instead of 4-16 h in previous in-solution methods). Reduction and alkylation steps were not required. The MCR allowed identification of ricin by signature peptides in all targeted mode injections performed, with a complete absence of carry-over in blank injections. The MCRs (interior volume ≈ 1 μL) have very low backpressure, allowing for trivial online coupling with commercial nanoLC-MS systems. The open tubular nature of the MCRs allowed for repeatable within/between-reactor preparation and performance.

Advances in organic polymer-based monolithic column technology for high-resolution liquid chromatography-mass spectrometry profiling of antibodies, intact proteins, oligonucleotides, and peptides

This review focuses on the preparation of organic polymer-based monolithic stationary phases and their application in the separation of biomolecules, including antibodies, intact proteins and protein isoforms, oligonucleotides, and protein digests. Column and material properties, and the optimization of the macropore structure towards kinetic performance are also discussed. State-of-the-art liquid chromatography-mass spectrometry biomolecule separations are reviewed and practical aspects such as ion-pairing agent selection and carryover are presented. Finally, advances in comprehensive two-dimensional LC separations using monolithic columns, in particular ion-exchange×reversed-phase and reversed-phase×reversed-phase LC separations conducted at high and low pH, are shown.

Characterization of an immobilized enzyme reactor for on-line protein digestion

Despite the developments for faster liquid chromatographic and mass spectral detection techniques, the standard in-solution protein digestion for proteomic analyses has remained relatively unchanged. The typical in-solution trypsin protein digestion is usually the slowest part of the workflow, albeit one of the most important. The development of a highly efficient immobilized enzyme reactor (IMER) with rapid performance for on-line protein digestion would greatly decrease the analysis time involved in a proteomic workflow. Presented here is the development of a silica based IMER for on-line protein digestion, which produced rapid digestions in the presence of organic mobile phase for both model proteins and a complex sample consisting of the insoluble portion of a yeast cell lysate. Protein sequence coverage and identifications evaluated between the IMER and in-solution digestions were comparable. Overall, for a yeast cell lysate with only a 10s volumetric residence time on-column, the IMER identified 507 proteins while the in-solution digestion identified 490. There were no significant differences observed based on identified protein's molecular weight or isoelectric point between the two digestion methods. Implementation of the IMER into the proteomic workflow provided similar protein identification results, automation for sample analysis, and reduced the analysis time by 15h.

Bioanalytical approaches for characterizing catabolism of antibody–drug conjugates

The in vivo stability and catabolism of antibody–drug conjugates (ADCs) directly impact their PK, efficacy and safety, and metabolites of the cytotoxic or small molecule drug component of an ADC can further complicate these factors. This perspective highlights the importance of understanding ADC catabolism and the associated bioanalytical challenges. We evaluated different bioanalytical approaches to qualitatively and quantitatively characterize ADC catabolites. Here we review and discuss the rationale and experimental strategies used to design bioanalytical assays for characterization of ADC catabolism and supporting ADME studies during ADC clinical development. This review covers both large and small molecule approaches, and uses examples from Kadcyla® (T-DM1) and a THIOMAB™ antibody–drug conjugate to illustrate the process.