Thermo-responsive adsorbent for size-selective protein adsorption

Multiple optimizations of recombinant plasmid for improving expression of Hepatitis B core antigen in Escherichia coli

Hepatitis B core antigen (HBcAg) can self-assemble into virus-like particles (VLPs) when expressed in Escherichia coli. We optimized the different of the expression plasmid pBV220, including the ribosome bind site (RBS), spacer region, promoter and replication origin (ori), as well as the hbc gene dosage, to enhance HBcAg transcription and translation in E. coli. The optimized construct with a customized RBS6, 6 nt spacer, T7 promoter and pUCori significantly increased the levels of HBc36GFP fusion protein to 3.4-folds compared to the control. Thereafter, we substituted hbc36gfp gene with different copies of the hbc gene and tested the effects of gene dosage on HBcAg expression. The HBcAg-VLPs yield obtained using an engineered strain with three copies of hbc was 842.1 ± 46.8 μg/mL, which was 2.2-folds higher compared to that in the control strain. Thus, our study provides a simple and effective strategy for improving HBcAg expression in E. coli. Since the HBcAg-VLPs are promising carriers for presenting foreign antigen epitopes, an in vitro expression system that can generate high levels of HBcAg-VLPs can serve as a promising tool for developing novel HBV vaccines and drugs.

Smart Adsorbents for Aquatic Environmental Remediation

A noticeable interest and steady rise in research studies reporting the design and assessment of smart adsorbents for sequestering aqueous metal ions and xenobiotics has occurred in the last decade. This motivates compiling and reviewing the characteristics, potentials, and performances of this new adsorbent generation's metal ion and xenobiotics sequestration. Herein, stimuli-responsive adsorbents that respond to its media (as internal triggers; e.g., pH and temperature) or external triggers (e.g., magnetic field and light) are highlighted. Readers are then introduced to selective adsorbents that selectively capture materials of interest. This is followed by a discussion of self-healing and self-cleaning adsorbents. Finally, the review ends with research gaps in material designs.

Functional cellulose nanocrystals containing cationic and thermo-responsive polymer brushes

Cationic and thermo-responsive polymer brushes were grafted from the surface of cellulose nanocrystals. Di(ethylene glycol) methyl ether methacrylate (MEO₂MA) and poly(oligoethylene glycol) methyl ether acrylate (OEGMA₃₀₀) and (2-methacryloyloxyethyl) trimethylammonium chloride (DMC) were grafted from cellulose nanocrystals (CNCs) via free radical polymerization. The CNC-g-POEGMA (CP) possessed a tunable lower critical solution temperature (LCST) of about 50 °C, and cloud point measurements confirmed that the LCST of the nanoparticles could be manipulated within the range of 40-47 °C by adjusting the DMC content. The salt effect was also investigated, and the results revealed a typical salting-out effect for the CNC-g-POEGMA after the introduction of KCl. On the other hand, the CNC-g-POEGMA-g-DMC (CPD) copolymers displayed two salt-responsive characteristics; polyelectrolyte effect at lower salt concentrations, followed by the salting-out effect at higher salt concentrations, which is dependent on the DMC content.

Purification of the Recombinant Green Fluorescent Protein Using Aqueous Two-Phase System Composed of Recyclable CO2-Based Alkyl Carbamate Ionic Liquid

The formation of aqueous two-phase system (ATPS) with the environmentally friendly and recyclable ionic liquid has been gaining popularity in the field of protein separation. In this study, the ATPSs comprising N,N-dimethylammonium N′,N′-dimethylcarbamate (DIMCARB) and thermo-responsive poly(propylene) glycol (PPG) were applied for the recovery of recombinant green fluorescent protein (GFP) derived from Escherichia coli. The partition behavior of GFP in the PPG + DIMCARB + water system was investigated systematically by varying the molecular weight of PPG and the total composition of ATPS. Overall, GFP was found to be preferentially partitioned to the hydrophilic DIMCARB-rich phase. An ATPS composed of 42% (w/w) PPG 1000 and 4.4% (w/w) DIMCARB gave the optimum performance in terms of GFP selectivity (1,237) and yield (98.8%). The optimal system was also successfully scaled up by 50 times without compromising the purification performance. The bottom phase containing GFP was subjected to rotary evaporation of DIMCARB. The stability of GFP was not affected by the distillation of DIMCARB, and the DIMCARB was successfully recycled in three successive rounds of GFP purification. The potential of PPG + DIMCARB + water system as a sustainable protein purification tool is promising.

Size-selective purification of hepatitis B virus-like particle in flow-through chromatography: Types of ion exchange adsorbent and grafted polymer architecture

Hepatitis B virus-like particles expressed in Escherichia coli were purified using anion exchange adsorbents grafted with polymer poly(oligo(ethylene glycol) methacrylate) in flow-through chromatography mode. The virus-like particles were selectively excluded, while the relatively smaller sized host cell proteins were absorbed. The exclusion of virus-like particles was governed by the accessibility of binding sites (the size of adsorbents and the charge of grafted dextran chains) as well as the architecture (branch-chain length) of the grafted polymer. The branch-chain length of grafted polymer was altered by changing the type of monomers used. The larger adsorbent (90 μm) had an approximately twofold increase in the flow-through recovery, as compared to the smaller adsorbent (30 μm). Generally, polymer-grafted adsorbents improved the exclusion of the virus-like particles. Overall, the middle branch-chain length polymer grafted on larger adsorbent showed optimal performance at 92% flow-through recovery with a purification factor of 1.53. A comparative study between the adsorbent with dextran grafts and the polymer-grafted adsorbent showed that a better exclusion of virus-like particles was achieved with the absorbent grafted with inert polymer. The grafted polymer was also shown to reduce strong interaction between binding sites and virus-like particles, which preserved the particles' structure.

ε-Polylysine-based thermo-responsive adsorbents for immunoglobulin adsorption-desorption under mild conditions

Thermo-responsive adsorbents for immunoglobulin G (IgG) employing ε-polylysine (EPL) as a polymer backbone were developed. The introduction of mercaptoethylpyridine (MEP) as an IgG-binding ligand and hydrophobization of side chains afforded thermo-responsive IgG adsorbents, whose thermo-responsive IgG desorption ratio was up to 88% (EPL/MEP derivative 3m). The changes in surface densities of active MEP groups, which are caused by thermal conformational changes of the adsorbents, play key roles for IgG desorption. Although a trade-off of IgG adsorption capacity and IgG desorption ratio was observed, the present study offers a novel molecular design for thermo-responsive adsorbents with high synthetic accessibility and potentially low toxicity.

Upper critical solution temperature (UCST) phase transition of halide salts of branched polyethylenimine and methylated branched polyethylenimine in aqueous solutions

The upper critical solution temperature (UCST) phase transition of halide salts of branched polyethylenimine (PEI) and methylated branched polyethylenimine (MPEI) is first reported in aqueous solutions. In particular, iodide counter-ions can introduce UCST properties in MPEI. The importance of the counter-ion composition of MPEI for UCST transition is discussed in detail.