Expression of the Biologically Active Insulin Analog SCI-57 in Nicotiana Benthamiana

Amyloid Fibrillation of Insulin: Amelioration Strategies and Implications for Translation

Insulin is a therapeutically relevant molecule with use in treating diabetes patients. Unfortunately, it undergoes a range of untoward and often unpredictable physical transformations due to alterations in its biochemical environment, including pH, ionic strength, temperature, agitation, and exposure to hydrophobic surfaces. The transformations are prevalent in its physiologically active monomeric form, while the zinc cation-coordinated hexamer, although physiologically inactive, is stable and less susceptible to fibrillation. The resultant molecular reconfiguration, including unfolding, misfolding, and hydrophobic interactions, often results in agglomeration, amyloid fibrillogenesis, and precipitation. As a result, a part of the dose is lost, causing a compromised therapeutic efficacy. Besides, the amyloid fibrils form insoluble deposits, trigger immunologic reactions, and harbor cytotoxic potential. The physical transformations also hold back a successful translation of non-parenteral insulin formulations, in addition to challenges related to encapsulation, chemical modification, purification, storage, and dosing. This review revisits the mechanisms and challenges that drive such physical transformations in insulin, with an emphasis on the observed amyloid fibrillation, and presents a critique of the current amelioration strategies before prioritizing some future research objectives.

The Major Peanut Allergen Ara h 2 Produced in Nicotiana benthamiana Contains Hydroxyprolines and Is a Viable Alternative to the E. Coli Product in Allergy Diagnosis

Peanut allergy is a potentially life-threatening disease that is mediated by allergen-specific immunoglobulin E (IgE) antibodies. The major peanut allergen Ara h 2, a 2S albumin seed storage protein, is one of the most dangerous and potent plant allergens. Ara h 2 is posttranslationally modified to harbor four disulfide bridges and three hydroxyprolines. These hydroxyproline residues are required for optimal IgE-binding to the DPYSPOHS motifs representing an immunodominant IgE epitope. So far, recombinant Ara h 2 has been produced in Escherichia coli, Lactococcus lactis, Trichoplusia ni insect cell, and Chlamydomonas reinhardtii chloroplast expression systems, which were all incapable of proline hydroxylation. However, molecular diagnosis of peanut allergy is performed using either natural or E. coli-produced major peanut allergens. As IgE from the majority of patients is directed to Ara h 2, it is of great importance that the recombinant Ara h 2 harbors all of its eukaryotic posttranslational modifications. We produced hydroxyproline-containing and correctly folded Ara h 2 in the endoplasmic reticulum of leaf cells of Nicotiana benthamiana plants, using the plant virus-based magnICON® transient expression system with a yield of 200 mg/kg fresh biomass. To compare prokaryotic with eukaryotic expression methods, Ara h 2 was expressed in E. coli together with the disulfide-bond isomerase DsbC and thus harbored disulfide bridges but no hydroxyprolines. The recombinant allergens from N. benthamiana and E. coli were characterized and compared to the natural Ara h 2 isolated from roasted peanuts. Natural Ara h 2 outperformed both recombinant proteins in IgE-binding and activation of basophils via IgE cross-linking, the latter indicating the potency of the allergen. Interestingly, significantly more efficient IgE cross-linking by the N. benthamiana-produced allergen was observed in comparison to the one induced by the E. coli product. Ara h 2 from N. benthamiana plants displayed a higher similarity to the natural allergen in terms of basophil activation due to the presence of hydroxyproline residues, supporting so far published data on their contribution to the immunodominant IgE epitope. Our study advocates the use of N. benthamiana plants instead of prokaryotic expression hosts for the production of the major peanut allergen Ara h 2.

Transient Expression in Cytoplasm and Apoplast of Rotavirus VP6 Protein Fused to Anti-DEC205 Antibody in Nicotiana benthamiana and Nicotiana sylvestris

Rotavirus is the most common cause of severe diarrhea in infants and children worldwide and is responsible for about 215,000 deaths annually. Over 85% of these deaths originate in low-income/developing countries in Asia and Africa. Therefore, it is necessary to explore the development of vaccines that avoid the use of "living" viruses and furthermore, vaccines that have viral antigens capable of generating powerful heterotypic responses. Our strategy is based on the expression of the fusion of the anti-DEC205 single-chain variable fragment (scFv) coupled by an OLLAS tag to a viral protein (VP6) of Rotavirus in Nicotiana plants. It was possible to express transiently in N. benthamiana and N. sylvestris a recombinant protein consisting of the single chain variable fragment linked by an OLLAS tag to the VP6 protein. The presence of the recombinant protein, which had a molecular weight of approximately 75 kDa, was confirmed by immunodetection, in both plant species and in both cellular compartments (cytoplasm and apoplast) where it was expressed. In addition, the recombinant protein was modeled, and it was observed that some epitopes of interest are exposed on the surface, which could favor their immunogenic response.

Oral delivery of therapeutic proteins bioencapsulated in plant cells: preclinical and clinical advances

Oral delivery of protein drugs (PDs) made in plant cells could revolutionize current approaches of their production and delivery. Expression of PDs reduces their production cost by elimination of prohibitively expensive fermentation, purification, cold transportation/storage, and sterile injections and increases their shelf life for several years. Ability of plant cell wall to protect PDs from digestive acids/enzymes, commensal bacteria to release PDs in gut lumen after lysis of plant cell wall and role of GALT in inducing tolerance facilitate prevention or treatment allergic, autoimmune diseases or anti-drug antibody responses. Delivery of functional proteins facilitate treatment of inherited or metabolic disorders. Recent advances in making PDs free of antibiotic resistance genes in edible plant cells, long-term storage at ambient temperature maintaining their efficacy, production in cGMP facilities, IND enabling studies for clinical advancement and FDA approval of orally delivered PDs augur well for advancing this novel drug delivery platform technology.

Bringing New Methods to the Seed Proteomics Platform: Challenges and Perspectives

For centuries, crop plants have represented the basis of the daily human diet. Among them, cereals and legumes, accumulating oils, proteins, and carbohydrates in their seeds, distinctly dominate modern agriculture, thus play an essential role in food industry and fuel production. Therefore, seeds of crop plants are intensively studied by food chemists, biologists, biochemists, and nutritional physiologists. Accordingly, seed development and germination as well as age- and stress-related alterations in seed vigor, longevity, nutritional value, and safety can be addressed by a broad panel of analytical, biochemical, and physiological methods. Currently, functional genomics is one of the most powerful tools, giving direct access to characteristic metabolic changes accompanying plant development, senescence, and response to biotic or abiotic stress. Among individual post-genomic methodological platforms, proteomics represents one of the most effective ones, giving access to cellular metabolism at the level of proteins. During the recent decades, multiple methodological advances were introduced in different branches of life science, although only some of them were established in seed proteomics so far. Therefore, here we discuss main methodological approaches already employed in seed proteomics, as well as those still waiting for implementation in this field of plant research, with a special emphasis on sample preparation, data acquisition, processing, and post-processing. Thereby, the overall goal of this review is to bring new methodologies emerging in different areas of proteomics research (clinical, food, ecological, microbial, and plant proteomics) to the broad society of seed biologists.

Isolation and detection of a KDEL-tagged recombinant cholera toxin B subunit from Nicotiana benthamiana

Here we describe refined methods for the isolation and detection of a KDEL-tagged, plant-produced recombinant cholera toxin B subunit (CTB) that exhibits unique mucosal wound healing activity. The protein was transiently overexpressed in Nicotiana benthamiana, which generates some C-terminal KDEL truncated molecular species that are deficient in epithelial repair activity. With a new CHT chromatographical method described herein, these product-derived impurities were successfully separated from CTB with the intact KDEL sequence, as confirmed by mass spectrometry. In addition, an immunoassay capable of specifically detecting GM1 ganglioside-binding CTB with intact KDEL sequences was developed. Coupled together, these methods will aid in the quality control of KDEL-attached CTB produced in plant-based manufacturing systems towards a novel topical biotherapeutic for the treatment of acute and chronic mucosal inflammation.