Purification of green fluorescent protein using a two-intein system

Impacts of the -1 Amino Acid on Yeast Production of Protein-Intein Fusions

Expressing antibodies as fusions to the non-self-cleaving Mxe GyrA intein allows for site-specific chemical functionalization via expressed protein ligation. It is highly desirable to maximize the yield of functionalizable protein; and previously an evolved intein, 202-08, was identified that could increase protein fusion production in yeast. Given that the -1 amino acid residue upstream of inteins can affect cleavage efficiency, we examined the effects of amino acid variability at this position on 202-08 intein cleavage efficiency and secretion yield. Varying the -1 residue resulted in a wide range of cleavage behaviors with some amino acids yielding substantial autocleaved product that could not be functionalized. Autocleavage was noticeably higher with the 202-08 intein compared with the wild-type Mxe GyrA intein and resulted directly from the catalytic activity of the intein. Refeeding of production cultures with nitrogen base and casamino acids reduced, but did not eliminate autocleavage, while increasing protein-intein production up to seven-fold. Importantly, two amino acids, Gly and Ala, at the -1 position resulted in good cleavage efficiency with no undesirable autocleavage, and can be used in concert with refeeding strategies to increase total functionalizable protein yield for multiple protein fusion partners. Taken together, we describe an optimized yeast expression platform for protein-intein fusions. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2736, 2019.

Purification of a recombinant protein with cellulose-binding module 3 as the affinity tag

Easy-to-perform and low-cost protein purification methods are in high demand for the mass production of commonly used enzymes that play an important role in bioeconomy. A low-cost and rapid recombinant protein purification system was developed using CBM3 (family 3 cellulose-binding module) as affinity tag. This protocol describes the purification of CBM3-fusion protein and tag-free protein expressed in Pichia pastoris using CBM3 as an affinity tag.

Recombinant production of peptide C-terminal α-amides using an engineered intein

Peptides are of increasing interest as therapeutics in a wide range of diseases, including metabolic diseases such as diabetes and obesity. In the latter, peptide hormones such as peptide YY (PYY) and pancreatic peptide (PP) are important templates for drug design. Characteristic for these peptides is that they contain a C-terminal that is α-amidated, and this amidation is crucial for biological function. A challenge is to generate such peptides by recombinant means and particularly in a production scale. Here, we have examined an intein-mediated approach to generate a PYY derivative in a larger scale. Initially, we experienced challenges with hydrolysis of the intein fusion protein, which was reduced by a T3C mutation in the intein. Subsequently, we further engineered the intein to decrease the absolute size and improve the relative yield of the PYY derivative, which was achieved by substituting 54 residues of the 198 amino acid intein with an eight amino acid linker. The optimized intein construct was used to produce the PYY derivative under high cell density cultivation conditions, generating the peptide thioester precursor in good yields and subsequent amidation provided the target peptide.

Bacterial inclusion bodies as potential synthetic devices for pathogen recognition and a therapeutic substance release

Background

Adhesins of pathogens recognise the glycans on the host cell and mediate adherence. They are also crucial for determining the tissue preferences of pathogens. Currently, glyco-nanomaterials provide potential tool for antimicrobial therapy. We demonstrate that properly glyco-tailored inclusion bodies can specifically bind pathogen adhesins and release therapeutic substances.

Results

In this paper, we describe the preparation of tailored inclusion bodies via the conjugation of indicator protein aggregated to form inclusion bodies with soluble proteins. Whereas the indicator protein represents a remedy, the soluble proteins play a role in pathogen recognition. For conjugation, glutaraldehyde was used as linker. The treatment of conjugates with polar lysine, which was used to inactivate the residual glutaraldehyde, inhibited unwanted hydrophobic interactions between inclusion bodies. The tailored inclusion bodies specifically interacted with the SabA adhesin from Helicobacter pylori aggregated to form inclusion bodies that were bound to the sialic acids decorating the surface of human erythrocytes. We also tested the release of indicator proteins from the inclusion bodies using sortase A and Ssp DNAB intein self-cleaving modules, respectively. Sortase A released proteins in a relatively short period of time, whereas the intein cleavage took several weeks.

Conclusions

The tailored inclusion bodies are promising “nanopills” for biomedical applications. They are able to specifically target the pathogen, while a self-cleaving module releases a soluble remedy. Various self-cleaving modules can be enabled to achieve the diverse pace of remedy release.

Recombinant production of mGLP-1 by coupling of refolding and intein-mediated self-cleavage (CRIS)

Glucagon-like peptide-1 as an endogenous glucose-lowering peptide is a promising candidate for anti-diabetic drug development. Here, we developed a convenient method by coupling of refolding and intein-mediated self-cleavage (CRIS) to improve the recombinant production of a mutated glucagon-like peptide-1 (mGLP-1). Bacterial cell culture employing auto-induction was performed at 37 °C to avoid the intracellular self-cleavage of the intein fusion protein. The impacts of urea, pH, and temperature on the efficiency of CRIS were tested, and then, the optimized CRIS was established. Using the optimized method, we obtained the purified mGLP-1 with a yield of 3.41 mg peptide/g bacterial cells which was 5.6-fold higher than before. After that, using chromatography, peptide electrophoresis, and mass spectrometry, we determined the purity and molecular weight of the purified peptide and then confirmed its glucose-lowering activity by performing glucose tolerance test in mice. These results suggest that CRIS is a relatively simple and efficacious method for the recombinant production of mGLP-1, and as a general method, it can also be used for the recombinant preparation of some other proteins and peptides.

Inteins, valuable genetic elements in molecular biology and biotechnology

Inteins are internal protein elements that self-excise from their host protein and catalyze ligation of the flanking sequences (exteins) with a peptide bond. They are found in organisms in all three domains of life, and in viral proteins. Intein excision is a posttranslational process that does not require auxiliary enzymes or cofactors. This self-excision process is called protein splicing, by analogy to the splicing of RNA introns from pre-mRNA. Protein splicing involves only four intramolecular reactions, and a small number of key catalytic residues in the intein and exteins. Protein-splicing can also occur in trans. In this case, the intein is separated into N- and C-terminal domains, which are synthesized as separate components, each joined to an extein. The intein domains reassemble and link the joined exteins into a single functional protein. Understanding the cis- and trans-protein splicing mechanisms led to the development of intein-mediated protein-engineering applications, such as protein purification, ligation, cyclization, and selenoprotein production. This review summarizes the catalytic activities and structures of inteins, and focuses on the advantages of some recent intein applications in molecular biology and biotechnology.

The potential role of self-cleaving purification tags in commercial-scale processes

Purification tags are robust tools that can be used to purify a wide selection of target proteins, which makes them attractive candidates for implementation into platform processes. However, tag removal remains an expensive and significant issue that must be resolved before these tags can become widely used. One alternative is self-cleaving purification tags, which can provide the purity and versatility of conventional tags but eliminate the need for proteolytic tag removal. Many of these self-cleaving tags are based on inteins, but other emerging technologies, such as the FrpC and SrtAc proteins, have also been reported. In this review, we cover affinity and non-chromatographic self-cleaving purification tags and their potential industrial applications.

Recombinant chymosin used for exact and complete removal of a prochymosin derived fusion tag releasing intact native target protein

Fusion tags add desirable properties to recombinant proteins, but they are not necessarily acceptable in the final products. Ideally, fusion tags should be removed releasing the intact native protein with no trace of the tag. Unique endoproteinases with the ability to cleave outside their own recognition sequence can potentially cleave at the boundary of any native protein. Chymosin was recently shown to cleave a pro-chymosin derived fusion tag releasing native target proteins. In our hands, however, not all proteins are chymosin-resistant under the acidic cleavage conditions (pH 4.5) used in this system. Here, we have modified the pro-chymosin fusion tag and demonstrated that chymosin can remove this tag at more neutral pH (pH 6.2); conditions, that are less prone to compromise the integrity of target proteins. Chymosin was successfully used to produce intact native target protein both at the level of small and large-scale preparations. Using short peptide substrates, we further examined the influence of P1' amino acid (the N-terminus of the native target protein) and found that chymosin accepts many different, although not all, amino acids. We conclude that chymosin has several appealing characteristics for the exact removal of fusion tags. It is readily available in highly purified recombinant versions approved by the FDA for preparation of food for human consumption. We suggest that one should consider extending the use of chymosin to the preparation of pharmaceutical proteins.

Improved protein splicing reaction for low solubility protein fragments without insertion of native extein residues

Application of trans protein splicing has been limited both by solubility problems and by the insertion of native extein residues (NERs) at the splicing site. Here, we report two simple methods for overcoming these problems and increasing the yield and activity of the spliced product. First, low solubility was alleviated by adding arginine to the reaction buffer and optimizing the splicing reaction condition. The protocol was demonstrated in the context of a Green Fluorescent Protein variant (GFPuv), and the final yield was increased by 1.9-fold compared to control experiments performed under the same conditions but without addition of arginine. Second, the insertion of NERs was overcome by mutating, instead of inserting, a minimal number of residues in the target protein to amino acids required for the splicing reaction. We identified optimal splicing sites that conserve as much as possible the prerequisite NERs. As a result, the GFPuv residues 142-146 (EYNYN) were mutated to the reportedly minimal required NERs, EYCFN. GFPs spliced using this strategy had no NERs insertion and a fluorescence activity six times stronger than a control GFPuv with five NERs inserted at the splicing site (residue 145/6). In principle, the present protocol (Sw/oNI) can be applied to any target protein, even when no sequence similarity to NERs is present, though it will introduce up to five mutations at the splicing site.