A novel protein refolding method using a zeolite

Multifunctional synthetic nano-chaperone for peptide folding and intracellular delivery

Artificial, synthetic chaperones have attracted much attention in biomedical research due to their ability to control the folding of proteins and peptides. Here, we report bio-inspired multifunctional porous nanoparticles to modulate proper folding and intracellular delivery of therapeutic α-helical peptide. The Synthetic Nano-Chaperone for Peptide (SNCP) based on porous nanoparticles provides an internal hydrophobic environment which contributes in stabilizing secondary structure of encapsulated α-helical peptides due to the hydrophobic internal environments. In addition, SNCP with optimized inner surface modification not only improves thermal stability for α-helical peptide but also supports the peptide stapling methods in situ, serving as a nanoreactor. Then, SNCP subsequently delivers the stabilized therapeutic α-helical peptides into cancer cells, resulting in high therapeutic efficacy. SNCP improves cellular uptake and bioavailability of the anti-cancer peptide, so the cancer growth is effectively inhibited in vivo. These data indicate that the bio-inspired SNCP system combining nanoreactor and delivery carrier could provide a strategy to expedite the development of peptide therapeutics by overcoming existing drawbacks of α-helical peptides as drug candidates.

Molecular chaperones play an important part in protein folding and delivery in nature. Here, the authors report on the creation of a synthetic chaperone to control the folding of therapeutic peptides from random coil to alpha helix and demonstrate enhanced therapeutic potential in an in vivo tumour model.

Stacking of nanorings to generate nanotubes for acceleration of protein refolding

Self-assembly and photoisomerization of azobenzene-based amphiphilic molecules produced nanorings with an inner diameter of 25 nm and lengths of <40 nm. The nanorings, which consisted of a single bilayer membrane of the amphiphiles, retained their morphology in the presence of a stacking inhibitor; whereas in the absence of the inhibitor, the nanorings stacked into short nanotubes (<500 nm). When subjected to mild heat treatment, these nanotubes joined end-to-end to form nanotubes with lengths of several tens of micrometers. The nanorings and the short and long nanotubes were able to encapsulate proteins and thereby suppress aggregation induced by thermal denaturation. In addition, the nanotubes accelerated refolding of denatured proteins by encapsulating them and then releasing them into the bulk solution; refolding occurred simultaneously with release. In contrast, the nanorings did not accelerate protein refolding. Refolding efficiency increased with increasing nanotube length, indicating that the re-aggregation of the proteins was strictly inhibited by lowering the concentration of the proteins in the bulk solution as the result of the slow release from the longer nanotubes. The migration of the proteins through the long, narrow nanochannels during the release process will also contribute to refolding.

A zeolite as a tool for successful refolding of PEGylated proteins and their reassembly with tertiary structures

In the present study, we demonstrated zeolites' potential contribution to establish a method for preparing successfully refolded and reassembled PEGylated protein nanoparticles without the use of protein denaturants through the proteins' reassembly process. At first, the PEGylated nanoparticles are disassembled into identical PEGylated protein subunits by means of protein denaturants, and then the denatured subunits are adsorbed to zeolites. After the complete removal of denaturants, high-molecular-weight poly(ethylene glycol) (PEG) molecules are added to a solution where the zeolites suspend. Consequently, the PEGylated proteins are gradually reassembled into nanoparticles because the subunits are desorbed from the zeolites by the steric hindrance of the added PEG molecules. The present study reveals that PEGylated encapsulin was reassembled and hollow encapsulin nanoparticles were obtained. The results clearly demonstrate the usefulness of zeolites as a tool for the successful refolding of PEGylated proteins and their reassembly with tertiary structures.

Applications of zeolites in biotechnology and medicine – a review

Zeolites are microporous natural or synthetic tectosilicates, promising for organism detoxification, improvement of the nutrition status and immunity, separation of various biomolecules and cells, detection of biomarkers of various diseases, controlled drug and gene delivery, radical scavenging, haemostasis, tissue engineering and biomaterial coating.

Glycolipid-based nanostructures with thermal-phase transition behavior functioning as solubilizers and refolding accelerators for protein aggregates

The self-assembly of synthetic glycolipids produced nanostructures such as vesicles and nanotubes consisting of bilayer membranes, which underwent a gel-to-liquid crystalline thermal phase transition. Vesicles formed at temperatures above the thermal phase transition temperatures (T_g-l) could solubilize aggregates of denatured proteins by trapping them in the fluid bilayer membranes. Cooling to temperatures below T_g-l caused a morphological transformation into nanotubes that accompanied the thermal phase transition from the fluid to the solid state. This phenomenon allowed the trapped proteins to be quickly released into the bulk solution and simultaneously facilitated the refolding of the proteins. The refolding efficiency strongly depended on the electrostatic attraction between the bilayer membranes of the nanostructures and the proteins. Because of the long shape (>400 nm) of the nanotubes, simple membrane filtration through a pore size of 200 nm led to complete separation and recovery of the refolded proteins (3-9 nm sizes).

Clinoptilolite/PCL–PEG–PCL composite scaffolds for bone tissue engineering applications

The aim of this study was to prepare and characterize highly porous clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) composite scaffolds. Scaffolds with different clinoptilolite contents (10% and 20%) were fabricated with reproducible solvent-free powder compression/particulate leaching technique. The scaffolds had interconnective porosity in the range of 55–76%. Clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) scaffolds showed negligible degradation within eight weeks and displayed less water uptake and higher bioactivity than poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) scaffolds. The presence of clinoptilolite improved the mechanical properties. Highest compressive strength (5.6 MPa) and modulus (114.84 MPa) were reached with scaffold group containing 20% clinoptilolite. In vitro protein adsorption capacity of the scaffolds was also higher for clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) scaffolds. These scaffolds had 0.95 mg protein/g scaffold adsorption capacity and also higher osteoinductivity in terms of enhanced ALP, OSP activities and intracellular calcium deposition. Stoichiometric apatite deposition (Ca/P=1.686) was observed during cellular proliferation analysis with human fetal osteoblasts cells. Thus, it can be suggested that clinoptilolite/poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) composite scaffolds could be promising carriers for enhancement of bone regeneration in bone tissue engineering applications.

Effect of Photoinduced Size Changes on Protein Refolding and Transport Abilities of Soft Nanotubes

Self-assembly of azobenzene-modified amphiphiles (Glyn Azo, n=1-3) in water at room temperature in the presence of a protein produced nanotubes with the protein encapsulated in the channels. The Gly2 Azo nanotubes (7 nm internal diameter [i.d.]) promoted refolding of some encapsulated proteins, whereas the Gly3 Azo nanotubes (13 nm i.d.) promoted protein aggregation. Although the 20 nm i.d. channels of the Gly1 Azo nanotubes were too large to influence the encapsulated proteins, narrowing of the i.d. to 1 nm by trans-to-cis photoisomerization of the azobenzene units of the Gly1 Azo monomers packed in the solid bilayer membranes led to a squeezing out of the proteins into the bulk solution and simultaneously enhanced their refolding ratios. In contrast, photoinduced transformation of the Gly2 Azo nanotubes to short nanorings (<40 nm) with a large i.d. (28 nm) provided no further refolding assistance. We thus demonstrate that pertubation by the solid bilayer membrane wall of the nanotubes is important to accelerate refolding of the denatured proteins during their transport in the narrow nanotube channels.

Soft nanotube hydrogels functioning as artificial chaperones

Self-assembly of rationally designed asymmetric amphiphilic monomers in water produced nanotube hydrogels in the presence of chemically denatured proteins (green fluorescent protein, carbonic anhydrase, and citrate synthase) at room temperature, which were able to encapsulate the proteins in the one-dimensional channel of the nanotube consisting of a monolayer membrane. Decreasing the concentrations of the denaturants induced refolding of part of the encapsulated proteins in the nanotube channel. Changing the pH dramatically reduced electrostatic attraction between the inner surface mainly covered with amino groups of the nanotube channel and the encapsulated proteins. As a result, the refolded proteins were smoothly released into the bulk solution without specific additive agents. This recovery procedure also transformed the encapsulated proteins from an intermediately refolding state to a completely refolded state. Thus, the nanotube hydrogels assisted the refolding of the denatured proteins and acted as artificial chaperones. Introduction of hydrophobic sites such as a benzyloxycarbony group and a tert-butoxycarbonyl group onto the inner surface of the nanotube channels remarkably enhanced the encapsulation and refolding efficiencies based on the hydrophobic interactions between the groups and the surface-exposed hydrophobic amino acid residues of the intermediates in the refolding process. Refolding was strongly dependent on the inner diameters of the nanotube channels. Supramolecular nanotechnology allowed us to not only precisely control the diameters of the nanotube channels but also functionalize their surfaces, enabling us to fine-tune the biocompatibility. Hence, these nanotube hydrogel systems should be widely applicable to various target proteins of different molecular weights, charges, and conformations.

Strategies for successful recombinant expression of disulfide bond-dependent proteins in Escherichia coli

Bacteria are simple and cost effective hosts for producing recombinant proteins. However, their physiological features may limit their use for obtaining in native form proteins of some specific structural classes, such as for instance polypeptides that undergo extensive post-translational modifications. To some extent, also the production of proteins that depending on disulfide bridges for their stability has been considered difficult in E. coli.

Both eukaryotic and prokaryotic organisms keep their cytoplasm reduced and, consequently, disulfide bond formation is impaired in this subcellular compartment. Disulfide bridges can stabilize protein structure and are often present in high abundance in secreted proteins. In eukaryotic cells such bonds are formed in the oxidizing environment of endoplasmic reticulum during the export process. Bacteria do not possess a similar specialized subcellular compartment, but they have both export systems and enzymatic activities aimed at the formation and at the quality control of disulfide bonds in the oxidizing periplasm.

This article reviews the available strategies for exploiting the physiological mechanisms of bactera to produce properly folded disulfide-bonded proteins.

Use of zeolite to refold a disulfide-bonded protein

Zeolites are microporous crystalline aluminosilicates with a highly ordered structure. Using zeolite beta as an adsorbent, denatured/reduced hen egg lysozyme was refolded to the active form at high concentrations. The denatured/reduced lysozyme was adsorbed onto the zeolite and the protein was refolded by desorbing it into refolding buffer, consisting of redox reagents, guanidine hydrochloride, polyethylene glycol, and L-arginine. This zeolite refolding method could be highly effective for various kinds of proteins, refolding them with high efficiency even when they contain disulfide bonds.

Selective adsorption of bacterial cells onto zeolites

Zeolites adsorb microbial cells on their surfaces and selective adsorption for specific microorganisms was seen with certain zeolites. Tests for the adsorption ability of zeolites were conducted using various established microbial cell lines. Specific cell lines were shown to selectively absorb to certain zeolites, species to species. In order to understand the selectivity of adsorption, we tested adsorption under various pH conditions and determined the zeta-potentials of zeolites and cells. The adsorption of some cell lines depended on the pH, and some microorganisms were preferentially adsorbed at acidic pH. The values of zeta-potentials were used for calculating the electric double layer interaction energy between zeolites and microbial cells. There was a correlation between the experimental adsorption results and the interaction energy. Moreover, we evaluated the surface hydrophobicity of bacterial cells by using the microbial adherence to hydrocarbon (MATH) assay. In addition, we also applied this method for zeolites to quantify relative surface hydrophobicity. As a result, we found a correlation between the adsorption results and the hydrophobicity of bacterial cells and zeolites. These results suggested that adsorption could be explained mainly by electric double layer interactions and hydrophobic interactions. Finally, by using the zeolites Na-BEA and H-Y, we succeeded in clearly separating three representative microbes from a mixture of Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Zeolites could adsorb each of the bacterial cell species with high selectivity even from a mixed suspension. Zeolites can therefore be used as effective carrier materials to provide an easy, rapid and accurate method for cell separation.