Tamavidin, a versatile affinity tag for protein purification and immobilization

A reversible cell penetrating peptide-cargo linkage allows dissection of cell penetrating peptide- and cargo-dependent effects on internalization and identifies new functionalities of putative endolytic peptides

Cell penetrating peptides (CPPs) are a promising technology for therapeutic delivery of macromolecular cargos. CPPs have generally used covalent linkages to cargo, ensuring a common fate as one molecule. Conversely, our CPP-adaptor, TAT-CaM, noncovalently binds calmodulin binding sequence (CBS)-containing cargos in calcium rich media then dissociates in the calcium-poor endosomal environment following internalization, enhancing endosomal escape relative to standard CPPs. In this study, we report cell entry of positively charged protein cargos that were not increased by TAT-CaM while cargos based on the negatively charged maltose binding protein (MBP) displayed little intrinsic internalization but were internalized by TAT-CaM. In addition, association of positively charged proteins with negatively charged nucleic acids reduced internalization. This evidence points to the dominant role cargo charge plays in apparent CPP effectiveness. There has been little systematic investigation as to how interaction between CPPs and cargos impacts internalization efficiency. Our adaptors provide a tool that allows combinatorial assays to detect emergent properties. Toward this end we added 4 endolytic peptide (EP) sequences between cargo CBS and MBP moieties to create 4 new cargos and between TAT and CaM to create 4 new adaptors. The new cargos were assayed for internalization alone and with a panel of CPP-adaptors to identify combinations that displayed increased internalization efficiency or other properties. Among the most important results, addition of the EP LAH4 improved adaptor performance and provided some CPP capability to cargos. MBP-LAH4-CBS was internalized more effectively by most adaptors, suggesting this sequence has general stimulatory ability. Two other EPs, Aurein 1.2 and HA2, also provided some CPP capability to their MBP cargos but were unexpectedly antagonistic to internalization by most adaptors due to retention of adaptor/cargo complexes on the cell surface. We thus identified LAH4 as stimulator of internalization in both adaptors and cargos and uncovered new functionality for Aurein 1.2 and HA2, which may be related to their identification as EPs. Future experiments will test new endolytic capabilities made possible with combinatorial approaches.

Metal organic framework encapsulated tamavidin-Gluc reporter: application in COVID-19 spike antigen bioluminescent immunoassay

Enzyme linked immunosorbent assay (ELISA) is one of the most utilized serological methods to diagnose and identify etiologic agents of many infectious diseases and other physiologically important analytes. ELISA can be used either alone or adjunct to other diagnostic methods such as molecular arrays, and other serological techniques. Most ELISA assays utilize reagents that are proteinaceous in nature, which are not very stable and require cold-chain transport systems. Development of a desirable immunoassay requires stability of reagents used and its ability to be stored at room temperature without sacrificing the activity of the reagents or the protein of interest. Metal organic frameworks (MOFs) are a rapidly emerging and evolving class of porous polymeric materials used in a variety of biosensor applications. In this study, we introduce the use of MOFs to stabilize a universal reporter fusion protein, specifically, avidin-like protein (Tam-avidin2) and the small bioluminescent protein Gaussia luciferase (Gluc) forming the fusion reporter, tamavidin2-Gluc (TA2-Gluc). This fusion protein serves as a universal reporter for any assays that utilize biotin-avidin binding strategy. Using SARS-CoV2 S1 spike antigen as the model target antigen, we demonstrated that encapsulation of TA2-Gluc fusion protein using a nano-porous material, zeolitic imidazolate framework-8 (ZIF-8), allows us to store and preserve this reporter protein at room temperature for over 6 months and use it as a reporter for an ELISA assay. Our optimized assay was validated demonstrating a 0.26 μg mL-1 limit of detection, high reproducibility of assay over days, detection of spiked non-virulent SARS-COV2 pseudovirus in real sample matrix, and detection in real COVID-19 infected individuals. This result can lead to the utilization of our TA2-Gluc fusion protein reporter with other assays and potentially in diagnostic technologies in a point-of-care setting.

Facile Synthesis and Characterization of a Novel Tamavidin-Luciferase Reporter Fusion Protein for Universal Signaling Applications

Despite the avidin/biotin reaction being one of the most ubiquitous noncovalent immobilization and sensing strategies in scientific research, the ability to synthesize useful amounts of biotin-binding fusion constructs is hampered by poor solubility in bacterial expression systems. As such, there are few reports of successful genetic reporter fusions incorporating a biotin-binding partner. To address this, a sensitivity-enhanced, synthetically facile reporter fusion is developed to merge the bioluminescence output of Gaussia luciferase (Gluc) with the recently characterized biotin-binding ability of tamavidin 2 (TA2) for general and universal signaling applications in biological and analytical systems. This fusion construct enables direct bacterial expression of a reporter system incorporating two important functionalities in a 1:1 stoichiometric relationship that can provide detection of discrete events at low concentrations. Using a cold-shock expression system, highly concentrated construct can be obtained from standard culture volumes while retaining essentially native protein activity. To demonstrate feasibility and provide an example application, this fusion construct is then included in a standard target-bridged assay design for the sensitive detection of four miRNA targets.

Photoactivable Elimination of Tumorigenic Human Induced Pluripotent Stem Cells by Using a Lectin-Doxorubicin Prodrug Conjugate

Human pluripotent stem cells (hPSCs) are attractive resources for regenerative medicine, but medical applications are hindered by their tumorigenic potential. Previously, a hPSC-specific lectin probe, rBC2LCN, was identified through comprehensive glycome analysis by using high-density lectin microarrays. Herein, a lectin-doxorubicin (DOX) prodrug conjugate, with controllable photolysis activation for the elimination of tumorigenic human induced pluripotent stem cells, has been developed. rBC2LCN was fused with a biotin-binding protein, tamavidin (BC2Tama), and the fusion protein was expressed in Escherichia coli and purified by means of affinity chromatography. BC2Tama was then conjugated with doxorubicin-photocleavable biotin (DOXPCB). The BC2Tama-DOXPCB conjugates were observed to bind to hPSCs followed by internalization. Upon exposure to ultraviolet light, DOX was released inside the cells, which allowed specific killing of the hPSCs. Thus, BC2Tama-DOXPCB should be useful for the targeted elimination of hPSCs contained in hPSC-derived cell therapy products. This is the first report of the generation of lectin-prodrug conjugates. BC2Tama should be applicable for the targeted delivery of various types of biotinylated compounds into hPSCs.

Amine Landscaping to Maximize Protein-Dye Fluorescence and Ultrastable Protein-Ligand Interaction

Chemical modification of proteins provides great opportunities to control and visualize living systems. The most common way to modify proteins is reaction of their abundant amines with N-hydroxysuccinimide (NHS) esters. Here we explore the impact of amine number and positioning on protein-conjugate behavior using streptavidin-biotin, a central research tool. Dye-NHS modification of streptavidin severely damaged ligand binding, necessitating development of a new streptavidin-retaining ultrastable binding after labeling. Exploring the ideal level of dye modification, we engineered a panel bearing 1–6 amines per subunit: “amine landscaping.” Surprisingly, brightness increased as amine number decreased, revealing extensive quenching following conventional labeling. We ultimately selected Flavidin (fluorophore-friendly streptavidin), combining ultrastable ligand binding with increased brightness after conjugation. Flavidin enhanced fluorescent imaging, allowing more sensitive and specific cell labeling in tissues. Flavidin should have wide application in molecular detection, providing a general insight into how to optimize simultaneously the behavior of the biomolecule and the chemical probe.

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Labeling of streptavidin with small-molecule dyes impairs ligand binding

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K121R mutation rescues ligand stability after dye labeling

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Landscaping of protein amines optimizes brightness

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Fluorophore-friendly streptavidin improves imaging specificity and sensitivity

Mycosynthesis of nanoparticles using edible and medicinal mushrooms

This review distinguishes myco-nanotechnology using metallic nanoparticles (meta-NPs) synthesized from edible mushroom matter. Green chemistry approaches were attempted to myco-synthesize meta-NPs (viz., Ag-NP, Au-NP, Se-NP, CdS-NP, Fe-NP, Pa-NP, and ZnS-NP) via different routes using edible mushrooms and have been tested toward 79% biomedical and 21% industrial applications. Biomaterials were used as biofactors to form metallic NPs. In mushroom science, mycomaterials of mushrooms were used at different percentages to mycosynthesize in an ecofriendly/green way; mycomaterials such as crude extracts of basidocarp (53%), mycelial extract or free cell filtrate (28%), in crude form or in purified form such as polysaccharides at different percentages; 9% (especially glucan), proteins/enzymes (7%) and polysaccharides protein complex (3%) as new research lines. Generally, in this field of mushroom nanoparticles about 84% of mycosynthesized NPs using mushrooms are placed outside the fungal cell (extracellular) and 16% are intracellular in the mushroom hyphae. The knowledge of the performance and influence of meta-NPs in edible mushrooms has developed in the last 10 years. Generally, while

Immobilized sialyltransferase fused to a fungal biotin-binding protein: Production, properties, and applications

A β-galactoside α2,6-sialyltransferase (ST) from the marine bacterium Photobacterium sp. JT-ISH-224 with a broad acceptor substrate specificity was fused to a fungal biotin-binding protein tamavidin 2 (TM2) to produce immobilized enzyme. Specifically, a gene for the fusion protein, in which ST from Photobacterium sp. JT-ISH-224 and TM2 were connected via a peptide linker (ST-L-TM2) was constructed and expressed in Escherichia coli. The ST-L-TM2 was produced in the soluble form with a yield of approximately 15,000 unit/300 ml of the E. coli culture. The ST-L-TM2 was partially purified and part of it was immobilized onto biotin-bearing magnetic microbeads. The immobilized ST-L-TM2 onto microbeads could be used at least seven consecutive reaction cycles with no observed decrease in enzymatic activity. In addition, the optimum pH and temperature of the immobilized enzyme were changed compared to those of a free form of the ST. Considering these results, it was strongly expected that the immobilized ST-L-TM2 was a promising tool for the production of various kind of sialoligosaccharides.

Recent advances on host plants and expression cassettes' structure and function in plant molecular pharming

Plant molecular pharming is a promising system to produce important recombinant proteins such as therapeutic antibodies, pharmaceuticals, enzymes, growth factors, and vaccines. The system provides an interesting alternative method to the direct extraction of proteins from inappropriate source material while offering the possibility to overcome problems related to product safety and source availability. Multiple factors including plant hosts, genes of interest, expression vector cassettes, and extraction and purification techniques play important roles in the plant molecular pharming. Plant species, as a biosynthesis platform, are a crucial factor in achieving high yields of recombinant protein in plant. The choice of recombinant gene and its expression strategy is also of great importance in ensuring a high amount of the recombinant proteins. Many studies have been conducted to improve expression, accumulation, and purification of the recombinant protein from molecular pharming systems. Re-engineered vectors and expression cassettes are also pivotal tools in enhancing gene expression at the transcription and translation level, and increasing protein accumulation, stability, retention and targeting of specific organelles. In this review, we report recent advances and strategies of plant molecular pharming while focusing on the choice of plant hosts and the role of some molecular pharming elements and approaches: promoters, codon optimization, signal sequences, and peptides used for upstream design, purification and downstream processing.

High-level expression of tamavidin 2 in human cells by codon-usage optimization

Tamavidin 2 is a fungal protein that binds to biotin with an extremely high affinity. Tamavidin 2 is superior to avidin or streptavidin in terms of its low-level non-specific binding and high-level thermal stability. However, the gene for tamavidin 2 is highly expressed in Escherichia coli but not in mammalian cells, restricting its application as an affinity tag in mammalian cells. Here, we optimized the codon usage of tamavidin 2 for human cells and found that the resultant mutant expressed tamavidin 2 at approximately 30-fold higher level compared with the native gene. The protein thus produced in human cells could be purified by iminobiotin affinity chromatography, bound tightly to biotin, and was stable at high temperature (82 °C). This powerful technology for high-level expression of tamavidin 2 in mammalian cells will be of value in evaluating various fusion proteins produced in mammalian cells for numerous applications.

Expression, purification, and immobilization of recombinant tamavidin 2 fusion proteins

Tamavidin 2 is a fungal avidin-like protein that binds biotin with high affinity. Unlike avidin or streptavidin, tamavidin 2 in soluble form is produced at high levels in Escherichia coli. In this chapter, we describe a method for immobilization and purification of recombinant proteins with the use of tamavidin 2 as an affinity tag. The protein fused to tamavidin 2 is tightly immobilized and simultaneously purified on biotinylated magnetic microbeads without loss of activity.

High efficiency acetylcholinesterase immobilization on DNA aptamer modified surfaces

We report here the in vitro selection of DNA aptamers for electric eel acetylcholinesterase (AChE). One selected aptamer sequence (R15/19) has a high affinity towards the enzyme (Kd=157±42 pM). Characterization of the aptamer showed its binding is not affected by low ionic strength (~20 mM), however significant reduction in affinity occurred at high ionic strength (~1.2 M). In addition, this aptamer does not inhibit the catalytic activity of AChE that we exploit through immobilization of the DNA on a streptavidin-coated surface. Subsequent immobilization of AChE by the aptamer results in a 4-fold higher catalytic activity when compared to adsorption directly on to plastic.

Fusion tags for protein solubility, purification and immunogenicity in Escherichia coli: the novel Fh8 system

Proteins are now widely produced in diverse microbial cell factories. The Escherichia coli is still the dominant host for recombinant protein production but, as a bacterial cell, it also has its issues: the aggregation of foreign proteins into insoluble inclusion bodies is perhaps the main limiting factor of the E. coli expression system. Conversely, E. coli benefits of cost, ease of use and scale make it essential to design new approaches directed for improved recombinant protein production in this host cell. With the aid of genetic and protein engineering novel tailored-made strategies can be designed to suit user or process requirements. Gene fusion technology has been widely used for the improvement of soluble protein production and/or purification in E. coli, and for increasing peptide's immunogenicity as well. New fusion partners are constantly emerging and complementing the traditional solutions, as for instance, the Fh8 fusion tag that has been recently studied and ranked among the best solubility enhancer partners. In this review, we provide an overview of current strategies to improve recombinant protein production in E. coli, including the key factors for successful protein production, highlighting soluble protein production, and a comprehensive summary of the latest available and traditionally used gene fusion technologies. A special emphasis is given to the recently discovered Fh8 fusion system that can be used for soluble protein production, purification, and immunogenicity in E. coli. The number of existing fusion tags will probably increase in the next few years, and efforts should be taken to better understand how fusion tags act in E. coli. This knowledge will undoubtedly drive the development of new tailored-made tools for protein production in this bacterial system.

Fusion tags for protein solubility, purification and immunogenicity in Escherichia coli: the novel Fh8 system

Proteins are now widely produced in diverse microbial cell factories. The Escherichia coli is still the dominant host for recombinant protein production but, as a bacterial cell, it also has its issues: the aggregation of foreign proteins into insoluble inclusion bodies is perhaps the main limiting factor of the E. coli expression system. Conversely, E. coli benefits of cost, ease of use and scale make it essential to design new approaches directed for improved recombinant protein production in this host cell. With the aid of genetic and protein engineering novel tailored-made strategies can be designed to suit user or process requirements. Gene fusion technology has been widely used for the improvement of soluble protein production and/or purification in E. coli, and for increasing peptide's immunogenicity as well. New fusion partners are constantly emerging and complementing the traditional solutions, as for instance, the Fh8 fusion tag that has been recently studied and ranked among the best solubility enhancer partners. In this review, we provide an overview of current strategies to improve recombinant protein production in E. coli, including the key factors for successful protein production, highlighting soluble protein production, and a comprehensive summary of the latest available and traditionally used gene fusion technologies. A special emphasis is given to the recently discovered Fh8 fusion system that can be used for soluble protein production, purification, and immunogenicity in E. coli. The number of existing fusion tags will probably increase in the next few years, and efforts should be taken to better understand how fusion tags act in E. coli. This knowledge will undoubtedly drive the development of new tailored-made tools for protein production in this bacterial system.

Tamavidin 2-HOT, a highly thermostable biotin-binding protein

Tamavidin 2 is a fungal tetrameric protein that binds with high affinity to biotin, like avidin and streptavidin. We replaced asparagine-115, which lies in a subunit-subunit interface of tamavidin 2, with cysteine to generate the novel, highly thermostable protein tamavidin 2-HOT. Tamavidin 2-HOT retained more than 80% of its biotin-binding activity even after incubation at 99.9°C for 60min and was fully active in 70% dimethylsulfoxide for 30min, whereas in these harsh conditions, avidin, streptavidin, and tamavidin 2 lost their activities (less than 20% of their biotin-binding activities). The Tm in which the biotin-binding activity becomes half of tamavidin 2-HOT was 105°C, at least 20°C higher than those of avidin, streptavidin, and tamavidin 2. Because a reducing agent removed the thermal stability of tamavidin 2-HOT, the N115C mutation likely created disulfide bridges that stabilized inter-subunit associations. Tamavidin 2-HOT is efficiently produced in the soluble form by Escherichia coli for practical use. The isoelectric point of tamavidin 2-HOT (7.4) is sufficiently low to reduce the chance for non-specific binding of non-target molecules due to high positive charges. Therefore, tamavidin 2-HOT may be useful in diverse novel applications that take advantage of its high biotin-binding capability that can withstand harsh conditions.

The Fh8 tag: a fusion partner for simple and cost-effective protein purification in Escherichia coli

Downstream processing is still a major bottleneck in recombinant protein production representing most of its costs. Hence, there is a continuing demand of novel and cost-effective purification processes aiming at the recovery of pure and active target protein. In this work, a novel purification methodology is presented, using the Fh8 solubility enhancer tag as fusion handle. The binding properties of Fh8 tag to a hydrophobic matrix were first studied via hydrophobic interaction chromatography (HIC). The Fh8 tag was then evaluated as a purification handle by its fusion to green fluorescent protein and superoxide dismutase. The purification efficiency of the Fh8-HIC strategy was compared to the immobilized metal ion affinity chromatography (IMAC) using the His6 tag. Results showed that the Fh8-HIC binding mechanism is calcium-dependent in a low salt medium, making the purification process highly selective. Both target proteins were biologically active, even when fused to Fh8, and were successfully purified by HIC, achieving efficiencies identical to those of IMAC. Thus, the Fh8 acts as an effective affinity tag that, together with its previously reported solubility enhancer capability, allows for the design of inexpensive and successful recombinant protein production processes in Escherichia coli.

Oriented immobilization of the tobacco etch virus protease for the cleavage of fusion proteins

The tobacco etch virus (TEV) protease is a useful tool for the removal of fusion tags from recombinant proteins. The difficulty in obtaining this enzyme led us to look for an optimal method for its use. In this work, we produced both the wild-type and the S219V mutant TEV proteases fused to the Streptag II affinity sequence (Streptag II-TEV(WT), and Streptag II-TEV(S219V), respectively). The two enzymes were affinity immobilized on a streptavidin-agarose matrix and compared to their respective free forms. Both immobilized Streptag II-TEV(WT) and Streptag II-TEV(S219V) were active on the 74-kDa Streptag II substrate with a retained activity of 83.5% and 81%, respectively compared to their free corresponding forms. The slight enzyme activity decrease caused by the immobilization was balanced by the enhanced stability and the successful repetitive use of the proteolytic columns. Thus, the wild-type and the mutant immobilized proteases were used, during a period of 18 months, for nine batch reactions with retention of 38% and 51% of their initial activities, respectively. The present results demonstrate that immobilized TEV protease on streptavidin-agarose is an attractive and efficient tool for fusion protein cleavage, especially when the target protein is fused to a streptagged fusion partner. Using this strategy, the total process can be shortened by performing the cleavage and the recovery of the purified target protein in one step.