Simplification of the purification of heat stable recombinant low molecular weight proteins and peptides from GST-fusion products

Improving Photocleavage Efficiency of Photocleavable Protein for Antimicrobial Peptide Histatin 1 Expression

BACKGROUND

Antimicrobial peptides (AMPs) are promising alternative agents for antibiotics to overcome antibiotic resistance problems. But, it is difficult to produce large-scale antimicrobial research due to the toxicity towards expression hosts or degradation by peptidases in the host. Therefore, heterologous recombinant expression of antimicrobial peptides has always been a challenging issue.

OBJECTIVES

To overcome toxicity to the expression host and low expression level, a new photocleavable protein fusion expression method for antimicrobial peptides is provided.3 Methods: Through directed evolution and high throughput screening, a photocleavable protein mutant R6-2-6-4 with a higher photocleavage efficiency was obtained. The DNA coding sequence of antimicrobial peptide Histatin 1 was fused within the sequence of R6-2-6-4 gene. The fusion gene was successfully expressed in Escherichia coli expression system.

RESULTS

Antimicrobial peptide Histatin 1 could be successfully expressed and purified by fusing within PhoCl mutant R6-2-6-4. The antimicrobial activity was rarely affected, and the MIC value was 33 ug/mL, which was basically equivalent to 32 ug/mL of the chemically synthesized Histatin 1. After amplification in a 5 L fermenter, the expression of PhoCl mutant (R6-2-6-4)-Histatin1 improved up to 87.6 mg/L in fermenter, and Histatin1 obtained by photocleavage also could up to 11 mg/L. The prepared Histatin1 powder remained stable when stored at 4oC for up to 4 months without any degradation. In addition, the expression and photocleavage of β -Defensin105 and Lysostaphin verified the certain universality of the PhoCl mutant fusion expression system.

CONCLUSION

Antimicrobial peptides Histatin 1, β -Defensin 105 and Lysostaphin were successfully expressed and purified by photocleavable protein mutant. This may provide a novel strategy to express and purify antimicrobial peptides in the Escherichia coli expression system.

Selective extraction of recombinant membrane proteins from Hansenula polymorpha by pulsed electric field and lytic enzyme pretreatment

BACKGROUND

In yeast, recombinant membrane proteins including viral scaffold proteins used for the formation of enveloped Virus-like particles (eVLPs) typically accumulate intracellularly. Their recovery is carried out by mechanical disruption of the cells, often in combination with detergent treatment. Cell permeabilization is an attractive alternative to mechanical lysis because it allows for milder and more selective recovery of different intracellular products.

RESULTS

Here, we present a novel approach for extraction of integral membrane proteins from yeast based on cell envelope permeabilization through a combination of pulsed electric field and lytic enzyme pretreatment of the cells. Our primary experiments focused on Hansenula polymorpha strain #25-5 co-expressing the integral membrane small surface protein (dS) of the duck hepatitis B virus and a fusion protein of dS with a trimer of a Human papillomavirus (HPV) L2-peptide (3xL2-dS). Irreversible plasma membrane permeabilization was induced by treating the cell suspension with monopolar rectangular pulses using a continuous flow system. The permeabilized cells were incubated with lyticase and dithiothreitol. This treatment increased the cell wall permeability, resulting in the release of over 50% of the soluble host proteins without causing significant cell lysis. The subsequent incubation with Triton X-100 resulted in the solubilization and release of a significant portion of 3xL2-dS and dS from the cells. By applying two steps: (i) brief heating of the cells before detergent treatment, and (ii) incubation of the extracts with KSCN, an 80% purity on the protein level has been achieved. Experiments performed with H. polymorpha strain T#3-3, co-expressing dS and the fusion protein EDIIIWNV-dS consisting of dS and the antigen from the West Nile virus (WSV), confirmed the applicability of this approach for recovering dS. The treatment, optimal for solubilization of 3xL2-dS and a significant part of dS, was not effective in isolating the fused protein EDIIIWNV-dS from the membranes, resulting in its retention within the cells.

CONCLUSIONS

This study presents an alternative approach for the recovery and partial purification of viral membrane proteins expressed in H. polymorpha. The factors influencing the effectiveness of this procedure and its potential use for the recovery of other integral membrane proteins are discussed.

Functional biology and biotechnology of thermophilic viruses

Viruses have developed sophisticated biochemical and genetic mechanisms to manipulate and exploit their hosts. Enzymes derived from viruses have been essential research tools since the first days of molecular biology. However, most viral enzymes that have been commercialized are derived from a small number of cultivated viruses, which is remarkable considering the extraordinary diversity and abundance of viruses revealed by metagenomic analysis. Given the explosion of new enzymatic reagents derived from thermophilic prokaryotes over the past 40 years, those obtained from thermophilic viruses should be equally potent tools. This review discusses the still-limited state of the art regarding the functional biology and biotechnology of thermophilic viruses with a focus on DNA polymerases, ligases, endolysins, and coat proteins. Functional analysis of DNA polymerases and primase-polymerases from phages infecting Thermus, Aquificaceae, and Nitratiruptor has revealed new clades of enzymes with strong proofreading and reverse transcriptase capabilities. Thermophilic RNA ligase 1 homologs have been characterized from Rhodothermus and Thermus phages, with both commercialized for circularization of single-stranded templates. Endolysins from phages infecting Thermus, Meiothermus, and Geobacillus have shown high stability and unusually broad lytic activity against Gram-negative and Gram-positive bacteria, making them targets for commercialization as antimicrobials. Coat proteins from thermophilic viruses infecting Sulfolobales and Thermus strains have been characterized, with diverse potential applications as molecular shuttles. To gauge the scale of untapped resources for these proteins, we also document over 20,000 genes encoded by uncultivated viral genomes from high-temperature environments that encode DNA polymerase, ligase, endolysin, or coat protein domains.

A Simple Purification Method for Heat-Stable Recombinant Low Molecular Weight Proteins and Peptides Via GST-Fusion Products

Here, we describe a simple, rapid, cost-effective, and efficient novel one-step purification method for GST-tagged peptides and small proteins. This novel technique applies to proteins and peptides that are known to be thermally stable at 60 °C and do not have elaborate structure(s) and whose heat-induced unfolding is reversible. This method takes advantage of glutathione S-transferase from Schistosoma japonicum (sj26GST) precipitating when heated at 60 °C. Purified GST-fusion products are subjected to enzymatic cleavage to separate the GST tag from the target peptide or small proteins. In our proposed method, the cleavage products are heated at 60 °C for 20 min which results in the precipitation of the GST tag. Subsequently, the GST tag is separated from the target peptide or small protein by high-speed centrifugation. Biophysical experiments such as SDS-PAGE, circular dichroism, isothermal titration calorimetry, mass spectroscopy, and multidimensional NMR spectroscopy confirm that the target peptides and small proteins are purified to more than 95% homogeneity, intact native conformation, and no significant change in the binding affinity of heat-treated purified product to the interacting partners.

Preparation of nickel-chelated iminodiacetate-functionalized macroporous agarose monolith using modular and clickable building blocks for affinity separation of histidine-tagged recombinant proteins

Selective separation and purification of protein from complex medium is required to completely investigate the structure and function of the target protein. In this study, a composite macroporous agarose monolith containing iminodiacetate-chelated Ni²⁺ ligands was synthesized for selective separation and purification of histidine-tagged recombinant proteins. The large and interconnected pores in the monolith enabled fast binding of proteins with high matrix tolerance in treating complex mediums. To realize the selective protein binding, the iminodiacetate was directly conjugated to epoxy-functionalized agarose monolith via simple chemical reactions between epoxy and imino groups. After chelated Ni²⁺, the composite monolith could bind histidine-tagged recombinant proteins through the coordination interaction between transition metal ions and the imidazole ring of histidine. To further increase the binding capacities of the monolith, a hydrophilic intermediate polymer chain containing multiple iminodiacetate immobilization sites was conjugated to the azide-functionalized agarose monolith via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The morphology and chemical composition of the composite agarose monolith were characterized systematically. The protein binding capacities of the obtained composite agarose monolith were subsequently investigated. The binding capacities of the composite agarose monolith towards the model proteins Gp10 and Lys84 were 0.93 and 0.51 mg/mL, respectively. The protein binding of the composite agarose monolith could be manipulated by adjusting the temperature and concentrations of imidazole. These results demonstrate that the composite agarose monolith could be used as an affinity medium for rapid separation and purification of histidine-tagged recombinant proteins from biological samples.