A fusion protein designed for noncovalent immobilization: stability, enzymatic activity, and use in an enzyme reactor

Vascular endothelial growth factor (VEGF) delivery approaches in regenerative medicine

The utilization of growth factors in the process of tissue regeneration has garnered significant interest and has been the subject of extensive research. However, despite the fervent efforts invested in recent clinical trials, a considerable number of these studies have produced outcomes that are deemed unsatisfactory. It is noteworthy that the trials that have yielded the most satisfactory outcomes have exhibited a shared characteristic, namely, the existence of a mechanism for the regulated administration of growth factors. Despite the extensive exploration of drug delivery vehicles and their efficacy in delivering certain growth factors, the development of a reliable predictive approach for the delivery of delicate growth factors like Vascular Endothelial Growth Factor (VEGF) remains elusive. VEGF plays a crucial role in promoting angiogenesis; however, the administration of VEGF demands a meticulous approach as it necessitates precise localization and transportation to a specific target tissue. This process requires prolonged and sustained exposure to a low concentration of VEGF. Inaccurate administration of drugs, either through off-target effects or inadequate delivery, may heighten the risk of adverse reactions and potentially result in tumorigenesis. At present, there is a scarcity of technologies available for the accurate encapsulation of VEGF and its subsequent sustained and controlled release. The objective of this review is to present and assess diverse categories of VEGF administration mechanisms. This paper examines various systems, including polymeric, liposomal, hydrogel, inorganic, polyplexes, and microfluidic, and evaluates the appropriate dosage of VEGF for multiple applications.

Multiple-Enzyme Graphene Microparticle Presenting Adaptive Chemical Network Capabilities

Interrelated reaction networks steered by multiple types of enzymes are among the most intriguing enzyme-based cellular features. These reaction networks display advanced features such as adaptation, stimuli-responsiveness, and decision-making in accordance with environmental cues. However, artificial enzyme particles are still deficient in network-level capabilities, mostly because delicate enzymes are difficult to immobilize and assemble. In this study, we propose a general strategy to prepare enzyme-based particles that demonstrate network reaction capability. We assembled multiple types of proteins with a nanoscopic binder prepared from polyelectrolyte and graphene. After assembly, the enzymes all preserved their catalytic capabilities. By incorporating multiple types of enzymes, the particles additionally displayed network-reaction capabilities. We were able to use NIR irradiations to quasi-reversibly adjust the catalytic abilities of these enzyme-based particles. In addition, after a biomimetic mineralization process was used to wrap the protein complexes in a MOF shell, the particles were more robust and catalytically active even after being immersed in acidic (pH 4) or basic (pH 10) solutions for 3 days. This study provides an insight into the study of network properties of functional enzyme particles experimentally and enriches scientific understanding of multifunctional or stimuli-responsive behaviors at the reaction network level. The building of artificial reaction networks possesses high potential in realizing intelligent microparticles that can perform complicated tasks.

Membrane Fusion and Infection of the Influenza Hemagglutinin

The influenza virus is a major health concern associated with an estimated 5000 to 30,000 deaths every year (Reed et al. 2015) and a significant economic impact with the development of treatments, vaccinations and research (Molinari et al. 2007). The entirety of the influenza genome is comprised of only eleven coding genes. An enormous degree of variation in non-conserved regions leads to significant challenges in the development of inclusive inhibitors for treatment. The fusion peptide domain of the influenza A hemagglutinin (HA) is a promising candidate for treatment since it is one of the most highly conserved sequences in the influenza genome (Heiny et al. 2007), and it is vital to the viral life cycle. Hemagglutinin is a class I viral fusion protein that catalyzes the membrane fusion process during cellular entry and infection. Impediment of the hemagglutinin's function, either through incomplete post-translational processing (Klenk et al. 1975; Lazarowitz and Choppin 1975) or through mutations (Cross et al. 2001), leads to non-infective virus particles. This review will investigate current research on the role of hemagglutinin in the virus life cycle, its structural biology and mechanism as well as the central role of the hemagglutinin fusion peptide (HAfp) to influenza membrane fusion and infection.

Polyionic and cysteine-containing fusion peptides as versatile protein tags

In response to advances in proteomics research and the use of proteins in medical and biotechnological applications, recombinant protein production and the design of specific protein characteristics and functions has become a widely used technology. In this context, protein fusion tags have been developed as indispensable tools for protein expression, purification, and the design of functionalized surfaces or artificially bifunctional proteins. Here we summarize how positively or negatively charged polyionic fusion peptides with or without an additional cysteine can be used as protein tags for protein expression and purification, for matrix-assisted refolding of aggregated protein, and for coupling of proteins either to technologically relevant matrices or to other proteins. In this context we used cysteine-containing polyionic fusion peptides for the design of immunotoxins. In general, polyionic fusion tags can be considered as a multifunctional module in protein technology.

Affinity-based release of chondroitinase ABC from a modified methylcellulose hydrogel

Chondroitinase ABC (ChABC) is a promising therapeutic for spinal cord injury as it can degrade the glial scar that is detrimental to regrowth and repair. However, the sustained delivery of bioactive ChABC is a challenge requiring highly invasive methods such as intra-spinal injections, insertion of intrathecal catheters, or implantation of delivery vehicles directly into the tissue. ChABC is thermally unstable, further complicating its delivery. Moreover, there are no commercial antibodies available for its detection. To achieve controlled release, we designed an affinity-based system that sustained the release of bioactive ChABC for at least 7days. ChABC was recombinantly expressed as a fusion protein with Src homology domain 3 (SH3) with an N-terminal histidine (HIS) tag and a C-terminal FLAG tag (ChABC-SH3). Protein purification was achieved using a nickel affinity column and, for the first time, direct quantification of ChABC down to 0.1nM was attained using an in-house HIS/FLAG double tag ELISA. The release of active ChABC-SH3 was sustained from a methylcellulose hydrogel covalently modified with an SH3 binding peptide. The rate of release was tunable by varying either the binding strength of the SH3-protein/SH3-peptide pair or the SH3-peptide to SH3-protein ratio. This innovative system has the potential to be used as a platform technology for the release and detection of other proteins that can be expressed using a similar construct.

Biomimetic enzyme nanocomplexes and their use as antidotes and preventive measures for alcohol intoxication

Organisms have sophisticated subcellular compartments containing enzymes that function in tandem. These confined compartments ensure effective chemical transformation and transport of molecules, and the elimination of toxic metabolic wastes. Creating functional enzyme complexes that are confined in a similar way remains challenging. Here we show that two or more enzymes with complementary functions can be assembled and encapsulated within a thin polymer shell to form enzyme nanocomplexes. These nanocomplexes exhibit improved catalytic efficiency and enhanced stability when compared with free enzymes. Furthermore, the co-localized enzymes display complementary functions, whereby toxic intermediates generated by one enzyme can be promptly eliminated by another enzyme. We show that nanocomplexes containing alcohol oxidase and catalase could reduce blood alcohol levels in intoxicated mice, offering an alternative antidote and prophylactic for alcohol intoxication.

Enzymatic hydrogelation to immobilize an enzyme for high activity and stability

This article describes a new way to immobilize an enzyme by enzymatic hydrogelation to facilitate catalysis in the organic solvent to attain high activity and stability. A self-immobilized acid phosphatase (AP) in a molecular hydrogel created by the enzymatic hydrogelation had shown higher activities in several organic solvents than those of free AP in the same solvents. The high activities of AP(gel) in organic solvents are mainly due to the cooperative effect of the amphiphilic nanofibers in the hydrogel and the phase transfer between the organic solvent and the water in the hydrogel. This approach provides a useful method to immobilize enzymes for biotransformation in organic solvents.

Matrix-assisted refolding of oligomeric small heat-shock protein Hsp26

Recombinant gene expression in the prokaryotic host Escherichia coli is of general interest for both biotechnology and basic research. Use of E. coli is inexpensive and advantageous due to the fully developed genetic accessibility. However, often insoluble target protein (inclusion body) accumulates in the cell. Especially when producing eukaryotic or disulfide bridged proteins in E. coli, inclusion body formation is observed. Nonetheless, insoluble protein can be regained and refolded in vitro. Commonly, renaturation of proteins is accomplished by methods involving dilution and/or dialysis. An interesting alternative is matrix-assisted refolding in which the denatured protein is refolded in the immobilized state. Here, matrix-assisted refolding was applied to refold a double cysteine variant of Hsp26, a small heat-shock protein from Saccharomyces cerevisiae which was insoluble after biosynthesis in E. coli BL21 (DE3) cells. This oligomeric protein was efficiently recovered from the insoluble fraction and refolded to its native oligomeric and chaperone-active state using ion exchange and size exclusion chromatography.

Functional Solubilization of Aggregation-prone HIV Envelope Proteins by Covalent Fusion with Chaperone Modules

The envelope proteins of human immunodeficiency virus (HIV) and human T-cell lymphotrophic virus (HTLV) mediate cell attachment and membrane fusion. For HIV-1, the precursor protein gp160 is cleaved proteolytically into two fragments, the surface-associated receptor binding subunit gp120 and the membrane spanning subunit gp41, which is involved in membrane fusion during virus entry. Soluble and immunoreactive variants of gp41 are essential for the reliable diagnosis of HIV-1 infections. Hitherto, gp41 was solubilized by adding detergents, or in acidic or alkaline solvents. We find that covalent fusions with SlyD or FkpA, two homodimeric Escherichia coli chaperones with peptidyl-prolyl isomerase activity, solubilize retroviral envelope proteins without compromising their immunological reactivity. gp41 from HIV-1, gp36 from HIV-2 and gp21 from HTLV could be expressed in large amounts in the Escherichia coli cytosol when fused with one or two subunits of SlyD or FkpA. The fusion proteins could be easily isolated and refolded, and showed high solubility and immunoreactivity, thus providing sensitive and reliable tools for diagnostic applications. Covalent fusions with SlyD or FkpA might be valuable generic tools for the solubilization and activation of aggregation-prone proteins.

Folding and refolding of proteins in chromatographic beds

The correct folding of solubilized recombinant proteins is of key importance for their production in industry. On-column refolding of proteins is mainly achieved by three methods: size-exclusion chromatography, ion exchange chromatography and affinity chromatography using immobilized metal chelates. The principles of these methods were first laid down in the 1990s, but many recent improvements have been made to these processes including sophisticated changes to the mobile phase composition and the recycling of aggregates to improve yield. Advances have also been made in the use of immobilized metal affinity chromatography and by mimicking the natural folding process with artificial chaperones.

Engineering of Escherichia coli to improve the purification of periplasmic Fab′ fragments: changing the pI of the chromosomally encoded PhoS/PstS protein

Escherichia coli is a widely used host for the heterologous expression of proteins of therapeutic and commercial interest. The scale and speed at which it can be cultured can result in the rapid generation of large quantities of product. However, to achieve low costs of production a simple and robust purification process is also required. The general factors that impact on the cost of a purification process are the scale at which a process can be performed, the cost of the purification matrix, and the number and complexity of the chromatographic steps employed. Purification of Fab' fragments of antibodies from the periplasm of E. coli using ion exchange chromatography can result in the co-purification of E. coli host proteins having similar functional pI: such as the periplasmic phosphate binding protein, PhoS/PstS. In such circumstances, an additional chromatographic step is required to separate Fab' from PhoS. Here, we change the functional pI of the chromosomally encoded PhoS/PstS to effect its non-purification with Fab' fragments, enabling the removal of an entire chromatographic step. This exemplifies the strategy of the modification of host proteins with the aim of simplifying the production of heterologous proteins.

GFP-visualized immobilized enzymes: degradation of paraoxon via organophosphorus hydrolase in a packed column

A versatile gene-fusion technique for immobilizing and visualizing biologically active enzymes which includes from the N to C-termini, an affinity histidine tag, the green fluorescent protein (GFP), a proteolytic enzyme (enterokinase, EK) cleavage site and the enzyme of interest, were developed. Specifically, the organophosphorus hydrolase was bound to the affinity (His(6))-reporter(GFP)-EK fusion elements. Organophosphorus hydrolase (OPH) is capable of degrading a variety of pesticides and nerve agents. In the case of immobilized OPH, paraoxon was rapidly degraded when pumped through a packed column. In reaction mixtures containing CHES buffer at pH 6.9, a continual decay in OPH activity was observed and importantly, this was monitored by GFP fluorescence. This decay in activity was fully restored, along with fluorescence, upon washing with PBS buffer. Many subsequent experiments were performed at varied pH and in different background buffer solutions. In all cases when there was OPH activity there was also marked fluorescence from the GFP fusion partner. Likewise, when OPH activity was lost, so was GFP fluorescence and, importantly, both were regenerated when washed in the presence of the kosmotropic salt, phosphate. Recently, Waldo et al. (1999) showed that GFP fluorescence from whole cells indicated the extent of proper folding of normally aggregated proteins designed via directed evolution. The present work demonstrates an application wherein GFP fluorescence indicates stability and activity of its fusion partner.

Applications of novel affinity cassette methods: use of peptide fusion handles for the purification of recombinant proteins

In this article, recent progress related to the use of different types of polypeptide fusion handles or 'tags' for the purification of recombinant proteins are critically discussed. In addition, novel aspects of the molecular cassette concept are elaborated, together with areas of potential application of these fundamental principles in molecular recognition. As evident from this review, the use of these concepts provides a powerful strategy for the high throughput isolation and purification of recombinant proteins and their derived domains, generated from functional genomic or zeomic studies, as part of the bioprocess technology leading to their commercial development, and in the study of molecular recognition phenomena per se. In addition, similar concepts can be exploited for high sensitivity analysis and detection, for the characterisation of protein bait/prey interactions at the molecular level, and for the immobilisation and directed orientation of proteins for use as biocatalysts/biosensors.

Polyionic fusion peptides function as specific dimerization motifs

The de novo design of a molecular adapter for directed association and covalent linkage of two polypeptides is presented. Using peptides containing charged amino acid residues and an additional cysteine residue (AlaCysLys(8) and AlaCysGlu(8)) we demonstrate that the electrostatic interaction promotes the association of two synthetic peptides and, subsequently, disulfide bond formation. The reaction depends on both the redox potential and on the ionic strength of the buffer. Varying the redox potential, the interaction of the peptides was quantified by a Delta G(0') of 6.6 +/- 0.2 kcal/mol. Heterodimerization of the peptides is highly specific, a competition of association by other cysteine containing compounds could not be observed. Two proteins comprising cysteine-containing polyionic fusion peptides, a modified Fab fragment and an alpha-glucosidase fusion, could be specifically conjugated by directed association and subsequent disulfide bond formation. Both proteins retain their functional characteristics within the bifunctional conjugate: enzymatic activity of the alpha-glucosidase and antigen-binding capacity of the Fab fragment are equivalent to the non-conjugated components.

Efficient enantioselective separation of drug enantiomers by immobilised antibody fragments

There is an increasing need for methods for efficient enantioselective separation and purification of chiral drugs. Genetic engineering provides the means for generating recombinant antibodies exhibiting extremely high specificity for even small molecular mass compounds. Here, recombinant antibody fragments have been generated for the drug diarylalkyltriazole that contains two chiral centres. Immobilised antibody fragments has been used successfully for efficient, step-wise separation of two enantiomers of the drug. Owing to the antibody specificity, one enantiomer came out in the flow-through, while the bound enantiomer could be specifically eluted. One of the antibodies tolerated solvents required both for dissolving the target molecules and for their elution for extended times and was shown to function over multiple cycles of the separation process.

Characterizing the functionality of recombinant T-cell receptors in vitro: a pMHC tetramer based approach

The very low affinity of the T-cell receptor (TCR) for the peptide-major histocompatibility complex (pMHC) has made it very challenging to design assays for testing the functionality of these molecules on small scales, which in turn has severely hampered the progress in developing expression and refolding methodologies for the TCR. We have now developed an ELISA assay for detecting pMHC binding to functional recombinant TCRs. It uses tetramers of biotinylated pMHCs bound to a neutravidin-horseradish peroxidase conjugate and detects the presence of functional TCR, bound in a productive orientation to an immobilized anti-Cbeta antibody. Specificity can be stringently demonstrated by inhibition with monomeric pMHCs. The assay is very sensitive and specific, and requires only very small amounts of protein. It has allowed us to study the unstable recombinant TCR P14, which we expressed and refolded from Escherichia coli. The TCR P14 is directed against the most abundant epitope of LCMV. We have confirmed the specificity of the interaction by BIAcore, and were able to determine the dissociation constant of the interaction of the P14 TCR and of the gp33-pMHC as 6 microM. This affinity ranks it among the tighter ones of TCR-pMHC interactions, and unusually low affinity thus does not seem to be the cause of the modest protective power of these T-cells, compared to others elicited in the anti-LCMV response. This strategy of multimerizing one partner and immobilizing the other in both a native form and productive orientation should be generally useful for characterizing the weak interactions of cell-surface molecules.

Purification of a viral coat protein by an engineered polyionic sequence

Virus-like particles composed of the polyoma coat protein VP1 were produced as a central building block of an artificial vector system for gene therapy. For this purpose, recombinant VP1 was expressed in E. coli. Classical purification schemes resulted only in low yields of protein. Therefore, we developed a new affinity purification procedure. We decided to use a polyionic sequence containing eight glutamic acid residues which allows efficient purification using ion-exchange chromatography. This peptide was inserted in a solvent exposed loop on the surface of VP1. After recombinant expression and cell lysis the first purification and concentration step consisted of a fractionated ammonium sulfate precipitation. The resuspended VP1 was loaded on an anion-exchange column. Elution with ca. 600 mM NaCl yielded almost homogeneous protein. Subsequently a size exclusion chromatography was performed to separate the pentameric VP1 from higher oligomeric and aggregated material. In contrast to wildtype VP1 the highly charged mutant form showed no significant tendency to aggregate. To demonstrate the functional state of the VP1 mutant, the in vitro assembly was investigated. At conditions similar to those for wildtype VP1 assembly, the mutant protein could form homogeneous virus-like particles.

Analysis of the dynamics of rhizomucor miehei lipase at different temperatures

The dynamics of Rhizomucor miehei lipase has been studied by molecular dynamics simulations at temperatures ranging from 200-500K. Simulations carried out in periodic boundary conditions and using explicit water molecules were performed for 400 ps at each temperature. Our results indicate that conformational changes and internal motions in the protein are significantly influenced by the temperature increase. With increasing temperature, the number of internal hydrogen bonds decreases, while surface accessibility, radius of gyration and the number of residues in random coil conformation increase. In the temperature range studied, the motions can be described in a low dimensional subspace, whose dimensionality decreases with increasing temperature. Approximately 80% of the total motion is described by the first (i) 80 eigenvectors at T=200K, (ii) 30 eigenvectors at T=300K and (iii) 10 eigenvectors at T=400K. At high temperature, the alpha-helix covering the active site in the native Rhizomucor miehei lipase, the helix at which end the active site is located, and in particular, the loop (Gly35-Lys50) show extensive flexibility.

The green fluorescent protein is a versatile reporter for bioprocess monitoring

The green fluorescent protein (GFP) of Aequorea victoria has become a convenient and versatile tool as a reporter protein in molecular cell biology and developmental biology. Here, it is shown that GFP may advantageously be used as a reporter system for bioprocess monitoring as well. Examples are given for monitoring fermentation as well as downstream processes for protein recovery. Thus, separation processes based on the application of affinity-fusion tags may be optimized in terms of the operational conditions by using GFP as a model target protein owing to facile screening by simple visual inspection. This item is discussed together with the presentation of a novel fusion tag with strong affinity for metal-chelate ligands: hisactophilin, a histidine-rich protein of Dictyostelium discoideum. This tag is of particular interest for affinity separation processes requiring multiple sites of interaction like aqueous and reverse micellar two-phase extraction as well as precipitation.

New applications for biocatalysts

Biocatalysis has always been a key focus area in biotechnology and new approaches for the utilization of biocatalysts have continued to emerge over the past year. Significant progress has been made in the biocatalytic production of both synthetic and natural polymers, in the generation of novel biocatalysts using genetic and biochemical approaches or through identification of new biological sources, in the immobilization of biocatalysts and their modification with amphiphilic polymers, and in the modulation of the stereochemistry of enzymatic reactions.

Strategies for achieving high-level expression of genes in Escherichia coli

Progress in our understanding of several biological processes promises to broaden the usefulness of Escherichia coli as a tool for gene expression. There is an expanding choice of tightly regulated prokaryotic promoters suitable for achieving high-level gene expression. New host strains facilitate the formation of disulfide bonds in the reducing environment of the cytoplasm and offer higher protein yields by minimizing proteolytic degradation. Insights into the process of protein translocation across the bacterial membranes may eventually make it possible to achieve robust secretion of specific proteins into the culture medium. Studies involving molecular chaperones have shown that in specific cases, chaperones can be very effective for improved protein folding, solubility, and membrane transport. Negative results derived from such studies are also instructive in formulating different strategies. The remarkable increase in the availability of fusion partners offers a wide range of tools for improved protein folding, solubility, protection from proteases, yield, and secretion into the culture medium, as well as for detection and purification of recombinant proteins. Codon usage is known to present a potential impediment to high-level gene expression in E. coli. Although we still do not understand all the rules governing this phenomenon, it is apparent that "rare" codons, depending on their frequency and context, can have an adverse effect on protein levels. Usually, this problem can be alleviated by modification of the relevant codons or by coexpression of the cognate tRNA genes. Finally, the elucidation of specific determinants of protein degradation, a plethora of protease-deficient host strains, and methods to stabilize proteins afford new strategies to minimize proteolytic susceptibility of recombinant proteins in E. coli.