Comparison of periplasmic and intracellular expression of Arabidopsis thionin proproteins in E. coli

Comparison of Periplasmic and Cytoplasmic Expression of Bovine Enterokinase Light Chain in E. coli

Enterokinase enzyme is widely used in production of recombinant proteins. This enzyme is isolated from the intestine and recognizes a specific cleavage site (X↓LYS-ASP₄). Several studies have been performed to produce recombinant active enterokinase. In this study, the coding sequence of bovine enteropeptidase light chain (bEK_L) was isolated from Iranian Sarabi cattle and its expression was investigated in the periplasm and cytoplasm of E. coli by two different expression vectors, pET22 and pET32RH. RNA was extracted from the duodenum part of cattle, cDNA was amplified, the enterokinase light chain coding fragment was cloned and the expression was examined by SDS-PAGE analysis. The higher amounts of soluble enterokinase as a fusion with thioredoxin (Trx) were detected in cytoplasmic expression. The functional enterokinase was purified with a yield of 45 mg per litter by two-steps Ni²⁺ affinity chromatography. The effective activity of the enzyme implies that it can be produced in large scale for biotechnological applications.

Analysis of a gene family for PDF-like peptides from Arabidopsis

Plant defensins are small, basic peptides that have a characteristic three-dimensional folding pattern which is stabilized by four disulfide bridges. We show here that Arabidopsis contains in addition to the proper plant defensins a group of 9 plant defensin-like (PdfL) genes. They are all expressed at low levels while GUS fusions of the promoters showed expression in most tissues with only minor differences. We produced two of the encoded peptides in E. coli and tested the antimicrobial activity in vitro. Both were highly active against fungi but had lower activity against bacteria. At higher concentrations hyperbranching and swollen tips, which are indicative of antimicrobial activity, were induced in Fusarium graminearum by both peptides. Overexpression lines for most PdfL genes were produced using the 35S CaMV promoter to study their possible in planta function. With the exception of PdfL4.1 these lines had enhanced resistance against F. oxysporum. All PDFL peptides were also transiently expressed in Nicotiana benthamiana leaves with agroinfiltration using the pPZP3425 vector. In case of PDFL1.4 this resulted in complete death of the infiltrated tissues after 7 days. All other PDFLs resulted only in various degrees of small necrotic lesions. In conclusion, our results show that at least some of the PdfL genes could function in plant resistance.

NMR structure and conformational dynamics of AtPDFL2.1, a defensin-like peptide from Arabidopsis thaliana

Plant defensins constitute the innate immune response against pathogens such as fungi and bacteria. Typical plant defensins are small, basic peptides that possess a characteristic three-dimensional fold stabilized by three or four disulfide bridges. In addition to known defensin genes, the Arabidopsis genome comprises >300 defensin-like genes coding for small cysteine-rich peptides. One of such genes encodes for AtPDFL2.1, a putative antifungal peptide of 55 amino acids, with six cysteine residues in its primary sequence. To understand the functional role of AtPDFL2.1, we carried out antifungal activity assays and determined its high-resolution three-dimensional structure using multidimensional solution NMR spectroscopy. We found that AtPDFL2.1 displays a strong inhibitory effect against Fusarium graminearum (IC₅₀≈4μM). This peptide folds in the canonical cysteine-stabilized αβ (CSαβ) motif, consisting of one α-helix and one triple-stranded antiparallel β-sheet stabilized by three disulfide bridges and a hydrophobic cluster of residues within its core where the α-helix packs tightly against the β-sheets. Nuclear spin relaxation measurements show that the structure of AtPDFL2.1 is essentially rigid, with the L3 loop located between β-strands 2 and 3 being more flexible and displaying conformational exchange. Interestingly, the dynamic features of loop L3 are conserved among defensins and are probably correlated to the antifungal and receptor binding activities.

Use of the SHuffle Strains in Production of Proteins

Escherichia coli continues to be a popular expression host for the production of proteins, yet successful recombinant expression of active proteins to high yields remains a trial and error process. This is mainly due to decoupling of the folding factors of a protein from its native host, when expressed recombinantly in E. coli. Failure to fold could be due to many reasons but is often due to lack of post-translational modifications that are absent in E. coli. One such post-translational modification is the formation of disulfide bonds, a common feature of secreted proteins. The genetically engineered SHuffle cells offer an expression solution to proteins that require disulfide bonds for their folding and activity. The purpose of this protocol unit is to familiarize the researcher with the biology of SHuffle cells and guide the experimental design in order to optimize and increase the chances of successful expression of their desired protein of choice. Example of the expression and purification of a model disulfide-bonded protein DsbC is described in detail. © 2016 by John Wiley & Sons, Inc.

Isolation and Characterization of a Thionin Proprotein-processing Enzyme from Barley

Thionins are plant-specific antimicrobial peptides that have been isolated from the endosperm and leaves of cereals, from the leaves of mistletoes, and from several other plant species. They are generally basic peptides with three or four disulfide bridges and a molecular mass of ~5 kDa. Thionins are produced as preproproteins consisting of a signal peptide, the thionin domain, and an acidic domain. Previously, only mature thionin peptides have been isolated from plants, and in addition to removal of the signal peptide, at least one cleavage processing step between the thionin and the acidic domain is necessary to release the mature thionin. In this work, we identified a thionin proprotein-processing enzyme (TPPE) from barley. Purification of the enzyme was guided by an assay that used a quenched fluorogenic peptide comprising the amino acid sequence between the thionin and the acidic domain of barley leaf-specific thionin. The barley TPPE was identified as a serine protease (BAJ93208) and expressed in Escherichia coli as a strep tag-labeled protein. The barley BTH6 thionin proprotein was produced in E. coli using the vector pETtrx1a and used as a substrate. We isolated and sequenced the BTH6 thionin from barley to confirm the N and C terminus of the peptide in planta. Using an in vitro enzymatic assay, the recombinant TPPE was able to process the quenched fluorogenic peptide and to cleave the acidic domain at least at six sites releasing the mature thionin from the proprotein. Moreover, it was found that the intrinsic three-dimensional structure of the BTH6 thionin domain prevents cleavage of the mature BTH6 thionin by the TPPE.

Self-processing of a barley subtilase expressed in E. coli

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The barley subtilase BAJ93208 has been expressed in the cytoplasm of E. coli C3030.

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Self processing occurred at the N and C-terminus.

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The Ser⁵⁵⁶Ala mutant was inactive and showed no self processing.

The barley protease BAJ93208 belongs to the subtilase family of serine proteases. We have expressed BAJ93208 in the cytoplasm of the Escherichiacoli strain SHuffle C3030 using a rhamnose-inducible promoter. The expression construct included a (His)₆-tag at the N-terminus and a strep-tag at the C-terminus. Western blot analysis revealed that the protein was processed at the N- and C-terminus. To exclude that this processing was due to contaminating E. coli proteases, a mutated BAJ93208 protease was constructed. This inactive mutant was not processed, demonstrating that the processing was an autocatalytic process. To define the exact cleavage sites mass spectrometry was used which detected four differently processed versions of the protease. At the N-terminus, the self-processing removed the internal inhibitor and an additional 19 amino acids. At the C-terminus there was a cleavage site after Ala⁷⁶⁵ which also removed the strep-tag. This explained the inability to detect the purified (His)₆-BAJ93208-strep protease with an anti-strep-tag antibody. Finally, an additional alanine was removed either at the N-terminus (Ala¹¹⁹) or at the C-terminus (Ala⁷⁶⁴).