Purification of inclusion bodies using PEG precipitation under denaturing conditions to produce recombinant therapeutic proteins from Escherichia coli

A protein standard absolute quantification strategy for enhanced absolute quantification of ricin in complex matrices using in vitro synthesized mutant holoprotein as internal standard by ultra-high-performance liquid chromatography-tandem mass spectrometry

Ricin is a highly toxic protein toxin that poses a potential bioterrorism threat due to its potency and widespread availability. However, the accurate quantification of ricin through absolute mass spectrometry (MS) using a protein standard absolute quantification (PSAQ) strategy is not widely practiced. This limitation primarily arises from the presence of interchain disulfide bonds, which hinder the production of full-length isotope-labeled ricin as an internal standard (IS) in vitro. In this study, we have developed a novel approach for the absolute quantification of ricin in complex matrices using recombinant single-chain and full-length mutant ricin as the protein IS, instead of isotope-labeled ricin, in conjunction with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The amino acid sequence of the ricin mutant internal standard (RMIS) was designed by introducing site mutations in specific amino acids of trypsin/Glu-C enzymatic digestion marker peptides of ricin. To simplify protein expression, the A-chain and B-chain of RMIS were directly linked to replace the original interchain disulfide bonds. The RMISs were synthesized using an Escherichia coli expression system. An appropriate RMIS was selected as the protein IS based on consistent digestion efficiency, UHPLC-MS/MS behavior, antibody recognition function, lectin activity, and proper depurination activity with intact ricin. The RMIS was utilized to simultaneously quantify A- and B-chain marker peptides of ricin through UHPLC-MS/MS. This method was thoroughly validated using a milk matrix. By employing internal protein standards, this quantitative strategy overcomes the challenges posed by variations in extraction recoveries, matrix effects, and digestion efficiency encountered when working with different matrices. Consequently, calibration curves generated from milk matrix-spiked samples were utilized to accurately and precisely quantify ricin in river water and plasma samples. Moreover, the established method successfully detected intact ricin in samples obtained from the sixth Organization for the Prohibition of Chemical Weapons (OPCW) exercise on biotoxin analysis. This study presents a novel PSAQ strategy that enables the accurate quantification of ricin in complex matrices.

Oxidation and reduction analysis of therapeutic recombinant human interleukin-15 by HPLC and LC-MS

Being an important immune stimulant of T lymphocytes and NK cells, the recombinant human interleukin-15 (rhIL-15) has been extensively researched in tumor immunotherapy or as a vaccine adjuvant. However, the rhIL-15 manufacturing level lags far behind its growing clinical demand due to the lack of efficient and exact analysis methodologies to characterize the trace by-products, typically redox and deamidation. In order to improve the production and quality control of rhIL-15, here we developed an expanded resolution reverse-phase high-performance liquid chromatography (ExRP-HPLC) approach to quickly and accurately analyze the oxidation and reduction by-products of rhIL-15, which may appear during the purification processes. Firstly, we developed RP-HPLC methods which can separate rhIL-15 fractions with different levels of oxidization or reduction, respectively, and the redox status of each peak was then determined by measuring the intact mass with a high-resolution mass spectrometer (UPLC-MS). To further clarify the complex pattern of oxidization of specific residues, the peaks with various oxidation levels were digested into pieces for peptide mapping to pinpoint the exact changes of oxygen and hydrogen atoms in the rhIL-15 by-products. In addition, we performed the ExRP-HPLC and UPLC-MS analysis of partially deamidated rhIL-15 to characterize their oxidation and reduction. Our work is the first in-depth characterization of the redox by-products of rhIL-15, even for deamidated impurities. The ExRP-HPLC method we reported can facilitate the rapid and accurate quality analysis of rhIL-15, which is substantially helpful for streamlining the industrial manufacturing of rhIL-15 to better meet the demands of clinical applications. KEYPOINTS: • The oxidization and reduction rhIL-15 by-products were characterized for the first time. • The changes of oxygen and hydrogen atoms in rhIL-15 redox by-products were accurately determined by UPLC-MS. • Oxidation and reduction by-products of deamidated rhIL-15 were further analyzed.

HBx represses WDR77 to enhance HBV replication by DDB1-mediated WDR77 degradation in the liver

Rationale: Hepatitis B x protein (HBx) is required to initiate and maintain the replication of hepatitis B virus (HBV). Protein arginine methyltransferases 5 (PRMT5) negatively regulates HBV transcription. WD repeat domain 77 protein (WDR77) greatly enhances the methyltransferase activity of PRMT5. However, the role of WDR77 in the modulation of cccDNA transcription and HBV replication is poorly understood. In this study, we investigated the mechanism by which HBx modulated HBV replication involving WDR77 in the liver.

Methods: A human liver-chimeric mouse model was established. Immunohistochemistry (IHC) staining, Western blot analysis, Southern blot analysis, Northern blot analysis, immunofluorescence assays, ELISA, RT-qPCR, CoIP assays, and ChIP assays were performed in human liver-chimeric mouse model, primary human hepatocytes (PHHs), HepG2-NTCP, dHepaRG and HepG2 cell lines.

Results: HBV infection and HBx expression remarkably reduced the protein levels of WDR77 in human liver-chimeric mice and HepG2-NTCP cells. WDR77 restricted cccDNA transcription and HBV replication in PHHs and HepG2-NTCP cells. Mechanically, WDR77 enhanced PRMT5-triggered symmetric dimethylation of arginine 3 on H4 (H4R3me2s) on the cccDNA minichromosome to control cccDNA transcription. HBx drove the cellular DDB1-containing E3 ubiquitin ligase to degrade WDR77 through recruiting WDR77, leading to the disability of methyltransferase activity of PRMT5. Thus, HBx promoted HBV replication by driving a positive feedback loop of HBx-DDB1/WDR77/PRMT5/H4R3me2s/cccDNA/HBV/HBx in the liver.

Conclusions: HBx attenuates the WDR77-mediated HBV repression by driving DDB1-induced WDR77 degradation in the liver. Our finding provides new insights into the mechanism by which HBx enhances HBV replication in the liver.

Development and characterization of a photo-cross-linked functionalized type-I collagen (Oreochromis niloticus) and polyethylene glycol diacrylate hydrogel

Collagen hydrogels have been widely investigated as scaffolds for tissue engineering due to their biocompatibility and capacity to promote cell adhesion. However, insufficient mechanical strength and rapid degradation properties remain the major obstacles for their applications. In the present study, type-I tilapia collagen (TC) was functionalized to form methacrylated tilapia collagen (MATC) by introducing methacrylic acid, developing a photo-cross-linked PEGDA-MATC hydrogel. The mechanical strength of PEGDA-MATC hydrogel could be tuned by adjusting the pH of the precursor solutions, which was decreased with the pH increased. At a pH 5 condition, PEGDA-MATC showed the highest compressive fracture stress (1.31 MPa). Compared to the PEGDA-TC hydrogel, PEGDA-MATC hydrogel exhibited similar swelling behavior to PEGDA-TC hydrogel in PBS solutions, but higher residual mass ratio (PEGDA-MATC, 213.2 ± 2.8%) than PEGDA-TC hydrogel (199.4 ± 3.8%) when cultured with type-I collagenase. PEGDA-MATC hydrogel showed sustained BSA release capacity for 6 days, and the BSA release ratio was significantly (p < 0.05) decreased with increasing concentration of loaded-BSA (68.6% at 4 mg mL^-1, 42.2% at 8 mg mL^-1). The PEGDA-MATC hydrogel allowed cell adhesion and proliferation in vitro. These results demonstrated that PEGDA-MATC hydrogel might be a potential scaffold for tissue engineering applications.

Molecular dynamics based improvement of the solubilizing self-cleavable tag Zbasic-ΔI-CM application in the preparation of recombinant proteins in Escherichia coli

Z_basic-ΔI-CM is a novel intein-based self-cleavable tag we developed to accelerate the soluble expression of recombinant proteins in Escherichia coli (E. coli). Previously we found that intein activity could be interfered by its flanking exteins, and thus reducing the production efficiency and final yield. In this work, we used CXC-chemokine 9 (CXCL9) as a model C-extein, which fusion with Z_basic-ΔI-CM showed high intein activity. When the fusion protein got soluble expression, CXCL9 was released immediately and purified directly from cell lysis supernatant. The results demonstrated that Z_basic-ΔI-CM tag had successfully mediated the efficient production of high-quality CXCL9 with reduced time and resources consumption in comparison with inclusion bodies expression. Molecular dynamics simulations suggested that the improved cleavage activity of Z_basic-ΔI-CM upon fusion with CXCL9 may be due to the higher dynamics of the first half loop and stabilization of the second half loop of intein. Our results proved that the self-cleavable Z_basic-ΔI-CM mediated soluble expression could be a feasible process for cytokines like CXCL9, thus of attractive potentials for production of therapeutic proteins using E. coli expression system.

Development of a recombinant human IL-15·sIL-15Rα/Fc superagonist with improved half-life and its antitumor activity alone or in combination with PD-1 blockade in mouse model

Recombinant human interleukin-15 (IL-15) is a potent cancer immunotherapeutic candidate due to its excellent immune stimulating effects. Previous work demonstrated that IL-15 appeared with short half-life in circulation system, while the complex with its receptor can prolong the half-life as well as benefit its activities in vivo. Therefore, IL-15 complex was more favorably considered for clinical development. Herein we developed IL-15·sIL-15Rα/Fc, a complex comprising of IL-15 and the extracellular region of its receptor alpha subunit which fused to Immunoglobulin G (IgG1) Fc to further prolong the half-life in plasma. Through transient gene expression in HEK293 cells, we expressed the superagonist by co-transfection of plasmids encoding IL-15 and sIL-15Rα/Fc respectively, yielding 36 mg/L of product after purification. Pharmacokinetic study demonstrated that the combination profoundly prolonged the half-life of IL-15 to 13.1 h in mice, about 18 folds longer than that of IL-15 monomer which is around 0.7 h. The bioactivity of the superagonist was characterized by CTLL-2 cells proliferation assay in vitro, showing its capability of stimulating the expansion of memory CD8⁺ T cells (cluster of differentiation) in mouse spleen. Using a HT-29 xenograft NOD-SCID mouse model, we observed tumor growth inhibition in all groups that received the superagonist, indicating its anti-tumor efficacy via stimulating infused human immune cells. In addition, combo cancer treatment by IL-15·sIL-15Rα/Fc and programmed death-1 (PD-1) antibody have shown stronger inhibitory effects as compared with treatment with either single molecule. Therefore, we developed IL-15·sIL-15Rα/Fc to be a long half-life potential cancer immunotherapy candidate that can be applied alone or in synergy with PD-1/PD-L1 blockade.

Highly efficient extraction and purification of low-density lipoprotein from hen egg yolk

Low-density lipoprotein (LDL) from hen egg yolk has high nutritional value and plays an important role in the fields of biology, medicine, and materials. To develop fundamental research about LDL, a highly efficient extraction method is necessary. We found that 30% saturated ammonium sulfate can extract more crude LDL than 40% saturation. We selected polyethylene glycol (PEG; nonionic type) to obtain crude LDL. Three factors were employed, namely, degree of polymerization, concentration of PEG, and pH of egg yolk plasma. The optimized condition was 5% PEG 4,000 and plasma pH 6.0, and the best extraction efficiency was 68.1 ± 0.5 g lipid /100 g DM and 69.9 ± 2.0% protein. The crude LDL oil of PEG precipitation was very significantly higher (P < 0.01) than ammonium sulfate precipitation (ASP), while there was no significant difference in protein, which indicates that PEG can extract more crude LDL. When ascorbic acid was added, hydrosulfuryl (SH) groups and lipids oxidation degree of crude LDL extracted by PEG (PEG-LDL) was very significantly lower than ASP (P < 0.01). We also obtained both purified LDL and yolk immunoglobulin (IgY) with an appropriate purification column. This paper proposes a highly efficient method to extract LDL with high activity using PEG and ensures co-purification of LDL and IgY.