Correct targeting of proinsulin in protein storage vacuoles of transgenic soybean seeds

Transgenic Soybean for Production of Thermostable α-Amylase

Alpha-amylases are crucial hydrolase enzymes which have been widely used in food, feed, fermentation, and pharmaceutical industries. Methods for low-cost production of α-amylases are highly desirable. Soybean seed, functioning as a bioreactor, offers an excellent platform for the mass production of recombinant proteins for its ability to synthesize substantial quantities of proteins. In this study, we generated and characterized transgenic soybeans expressing the α-amylase AmyS from Bacillus stearothermophilus. The α-amylase expression cassettes were constructed for seed specific expression by utilizing the promoters of three different soybean storage peptides and transformed into soybean via Agrobacterium-mediated transformation. The event with the highest amylase activity reached 601 U/mg of seed flour (one unit is defined as the amount of enzyme that generates 1 micromole reducing ends per min from starch at 65 °C in pH 5.5 sodium acetate buffer). The optimum pH, optimum temperature, and the enzymatic kinetics of the soybean expressed enzyme are similar to that of the E. coli expressed enzyme. However, the soybean expressed α-amylase is glycosylated, exhibiting enhanced thermostability and storage stability. Soybean AmyS retains over 80% activity after 100 min at 75 °C, and the transgenic seeds exhibit no significant activity loss after one year of storage at room temperature. The accumulated AmyS in the transgenic seeds represents approximately 15% of the total seed protein, or about 4% of the dry seed weight. The specific activity of the transgenic soybean seed flour is comparable to many commercial α-amylase enzyme products in current markets, suggesting that the soybean flour may be directly used for various applications without the need for extraction and purification.

Plant-made pharmaceuticals: exploring studies for the production of recombinant protein in plants and assessing challenges ahead

The production of pharmaceutical compounds in plants is attracting increasing attention, as plant-based systems can be less expensive, safer, and more scalable than mammalian, yeast, bacterial, and insect cell expression systems. Here, we review the history and current status of plant-made pharmaceuticals. Producing pharmaceuticals in plants requires pairing the appropriate plant species with suitable transformation technology. Pharmaceuticals have been produced in tobacco, cereals, legumes, fruits, and vegetables via nuclear transformation, chloroplast transformation, transient expression, and transformation of suspension cell cultures. Despite this wide range of species and methods used, most such efforts have involved the nuclear transformation of tobacco. Tobacco readily generates large amounts of biomass, easily accepts foreign genes, and is amenable to stable gene expression via nuclear transformation. Although vaccines, antibodies, and therapeutic proteins have been produced in plants, such pharmaceuticals are not readily utilized by humans due to differences in glycosylation, and few such compounds have been approved due to a lack of clinical data. In addition, achieving an adequate immune response using plant-made pharmaceuticals can be difficult due to low rates of production compared to other expression systems. Various technologies have recently been developed to help overcome these limitations; however, plant systems are expected to increasingly become widely used expression systems for recombinant protein production.

Soybean seed protein storage vacuoles for expression of recombinant molecules

Soybean is one of the most important protein sources for human consumption and livestock feed. Soy production also allows the biosynthesis of edible oils, biodiesel, and biofertilizers. With the advent of modern agricultural biotechnology, soybean plants have also converted into bioreactors of therapeutic proteins and industrial enzymes. Soybean's characteristics, such as protein storage vacuoles (PSVs) and other unique organelles, allow the plant to be exploited as an accumulator of heterologous proteins under high stability and scalability conditions, and that maintains its basic functions. This review reports the main aspects of heterologous protein accumulation in soybean PSVs.

Contributions of the international plant science community to the fight against human infectious diseases - part 1: epidemic and pandemic diseases

Infectious diseases, also known as transmissible or communicable diseases, are caused by pathogens or parasites that spread in communities by direct contact with infected individuals or contaminated materials, through droplets and aerosols, or via vectors such as insects. Such diseases cause ˜17% of all human deaths and their management and control places an immense burden on healthcare systems worldwide. Traditional approaches for the prevention and control of infectious diseases include vaccination programmes, hygiene measures and drugs that suppress the pathogen, treat the disease symptoms or attenuate aggressive reactions of the host immune system. The provision of vaccines and biologic drugs such as antibodies is hampered by the high cost and limited scalability of traditional manufacturing platforms based on microbial and animal cells, particularly in developing countries where infectious diseases are prevalent and poorly controlled. Molecular farming, which uses plants for protein expression, is a promising strategy to address the drawbacks of current manufacturing platforms. In this review article, we consider the potential of molecular farming to address healthcare demands for the most prevalent and important epidemic and pandemic diseases, focussing on recent outbreaks of high-mortality coronavirus infections and diseases that disproportionately affect the developing world.

Plant Platforms for Efficient Heterologous Protein Production

Production of recombinant proteins is primarily established in cultures of mammalian, insect and bacterial cells. Concurrently, concept of using plants to produce high-value pharmaceuticals such as vaccines, antibodies, and dietary proteins have received worldwide attention. Newer technologies for plant transformation such as plastid engineering, agroinfiltration, magnifection, and deconstructed viral vectors have been used to enhance the protein production in plants along with the inherent advantage of speed, scale, and cost of production in plant systems. Production of therapeutic proteins in plants has now a more pragmatic approach when several plant-produced vaccines and antibodies successfully completed Phase I clinical trials in humans and were further scheduled for regulatory approvals to manufacture clinical grade products on a large scale which are safe, efficacious, and meet the quality standards. The main thrust of this review is to summarize the data accumulated over the last two decades and recent development and achievements of the plant derived therapeutics. It also attempts to discuss different strategies employed to increase the production so as to make plants more competitive with the established production systems in this industry.

Evaluation of lettuce chloroplast and soybean cotyledon as platforms for production of functional bone morphogenetic protein 2

The bone morphogenetic protein BMP2 plays a crucial role in the formation and regeneration of bone and cartilage, which is critical for maintaining skeletal integrity and bone fracture repair. Because of its important role in osteogenic properties it has been commercially produced for clinical use. Here we report attempts to express human BMP2 using two plant systems (lettuce chloroplast and soybean seeds). The rhBMP2 gene (coding for the 13 kDa active polypeptide) was introduced in two regions of the lettuce chloroplast genome. Two homoplasmic events were achieved and RT-PCR demonstrated that the BMP2 gene was transcribed. However, it was not possible to detect accumulation of rhBMP2 in leaves. Two soybean events were achieved to express a full-length hBMP2 gene (coding for the 45 kDa pro-BMP2) fused with the α-coixin signal peptide, under control of the β-conglycinin promoter. Pro-BMP2 was expressed in the transgenic seeds at levels of up to 9.28% of the total soluble seed protein as determined by ELISA. It was demonstrated that this recombinant form was biologically active upon administration to C2C12 cell cultures, because it was able to induce an osteogenic cascade, as observed by the enhanced expression of SP7 (osterix) and ALPI (alkaline phosphatase) genes. Collectively, these results corroborated our previous observation that soybean seeds provide an effective strategy for achieving stable accumulation of functional therapeutic proteins, such as BMP2.

Transgenic Soybean Production of Bioactive Human Epidermal Growth Factor (EGF)

Necrotizing enterocolitis (NEC) is a devastating condition of premature infants that results from the gut microbiome invading immature intestinal tissues. This results in a life-threatening disease that is frequently treated with the surgical removal of diseased and dead tissues. Epidermal growth factor (EGF), typically found in bodily fluids, such as amniotic fluid, salvia and mother's breast milk, is an intestinotrophic growth factor and may reduce the onset of NEC in premature infants. We have produced human EGF in soybean seeds to levels biologically relevant and demonstrated its comparable activity to commercially available EGF. Transgenic soybean seeds expressing a seed-specific codon optimized gene encoding of the human EGF protein with an added ER signal tag at the N' terminal were produced. Seven independent lines were grown to homozygous and found to accumulate a range of 6.7 +/- 3.1 to 129.0 +/- 36.7 μg EGF/g of dry soybean seed. Proteomic and immunoblot analysis indicates that the inserted EGF is the same as the human EGF protein. Phosphorylation and immunohistochemical assays on the EGF receptor in HeLa cells indicate the EGF protein produced in soybean seed is bioactive and comparable to commercially available human EGF. This work demonstrates the feasibility of using soybean seeds as a biofactory to produce therapeutic agents in a soymilk delivery platform.

Effects of proteome rebalancing and sulfur nutrition on the accumulation of methionine rich δ-zein in transgenic soybeans

Expression of heterologous methionine-rich proteins to increase the overall sulfur amino acid content of soybean seeds has been only marginally successful, presumably due to low accumulation of transgenes in soybeans or due to gene silencing. Proteome rebalancing of seed proteins has been shown to promote the accumulation of foreign proteins. In this study, we have utilized RNAi technology to suppress the expression of the β-conglycinin, the abundant 7S seed storage proteins of soybean. Western blot and 2D-gel analysis revealed that β-conglycinin knockdown line (SAM) failed to accumulate the α', α, and β-subunits of β-conglycinin. The proteome rebalanced SAM retained the overall protein and oil content similar to that of wild-type soybean. We also generated transgenic soybean lines expressing methionine-rich 11 kDa δ-zein under the control of either the glycinin or β-conglycinin promoter. The introgression of the 11 kDa δ-zein into β-conglycinin knockdown line did not enhance the accumulation of the 11 kDa δ-zein. However, when the same plants were grown in sulfur-rich medium, we observed 3- to 16-fold increased accumulation of the 11 kDa δ-zein. Transmission electron microscopy observation revealed that seeds grown in sulfur-rich medium contained numerous endoplasmic reticulum derived protein bodies. Our findings suggest that sulfur availability, not proteome rebalancing, is needed for high-level accumulation of heterologous methionine-rich proteins in soybean seeds.

A strategy for targeting recombinant proteins to protein storage vacuoles by fusion to Brassica napus napin in napin-depleted seeds

Seeds are capable of accumulating high levels of seed storage proteins (SSP), as well as heterologous proteins under certain conditions. Arabidopsis thaliana was used to develop a strategy to deplete seeds of an endogenous SSP and then replenish them with the same protein fused to a heterologous protein. In several other studies, competition with endogenous SSP for space and metabolic resources was shown to affect the accumulation of recombinant proteins in seeds. We used RNAi to reduce the expression of the five napin genes and deplete the seeds of this SSP. Targeting a recombinant protein to a vacuole or structure within the seed where it can be protected from cytosolic proteases can also promote its accumulation. To achieve this, a synthetic Brassica napus napin gene (Bn napin) was designed that was both impervious to the A. thaliana napin (At napin) RNAi construct and permitted fusion to a heterologous protein, in this case green fluorescent protein (GFP). GFP was placed in several strategic locations within Bn napin with consideration to maintaining structure, processing sites and possible vacuolar targeting signals. In transgenic A. thaliana plants, GFP was strongly localized to the seed protein storage vacuole in all Bn napin fusion configurations tested, but not when expressed alone. This SSP depletion-replenishment strategy outlined here would be applicable to expression of recombinant proteins in industrial crops that generally have large repertoires of endogenous SSP genes.

A Vigna radiata 8S globulin α' promoter drives efficient expression of GUS in Arabidopsis cotyledonary embryos

Plants are proven effective bioreactors for the production of heterologous proteins including those desired by the biopharmaceutical industry. However, the potential of plants as bioreactors is limited by the availability of characterized plant promoters that can drive target gene expression in relatively distant plant species. Seeds are ideal for protein storage because seed proteins can be kept stably for several months. Hence, a strong promoter that can direct the expression and accumulation of target proteins within seeds represents a powerful tool in plant biotechnology. Toward this end, an effort was made to identify such a promoter from Vigna radiata (mung bean) to drive expression in dicot seeds. A 784-bp 5'-flanking sequence of the gene encoding the 8S globulin α' subunit (8SGα') of the V. radiata seed storage protein was isolated by genome walking. When the 5'-flanking region was analyzed with bioinformatics tools, numerous putative cis-elements were identified. The Green Fluorescent Protein (GFP) regulated by this promoter was observed to be transiently expressed in protoplasts derived from V. radiata cotyledons. Finally, transgenic Arabidopsis plants expressing the β-glucuronidase (GUS) reporter gene driven from the 8S globulin α' promoter showed strong GUS expression in transgenic embryos in both histochemical and quantitative GUS assays, confirming high expression within seeds. Therefore, the V. radiata 8S α' promoter has shown potential in directing expression in seeds for bioreactor applications.

NanoUPLC-MSE proteomic data assessment of soybean seeds using the Uniprot database

BACKGROUND

Recombinant DNA technology has been extensively employed to generate a variety of products from genetically modified organisms (GMOs) over the last decade, and the development of technologies capable of analyzing these products is crucial to understanding gene expression patterns. Liquid chromatography coupled with mass spectrometry is a powerful tool for analyzing protein contents and possible expression modifications in GMOs. Specifically, the NanoUPLC-MSE technique provides rapid protein analyses of complex mixtures with supported steps for high sample throughput, identification and quantization using low sample quantities with outstanding repeatability. Here, we present an assessment of the peptide and protein identification and quantification of soybean seed EMBRAPA BR16 cultivar contents using NanoUPLC-MSE and provide a comparison to the theoretical tryptic digestion of soybean sequences from Uniprot database.

RESULTS

The NanoUPLC-MSE peptide analysis resulted in 3,400 identified peptides, 58% of which were identified to have no miscleavages. The experiment revealed that 13% of the peptides underwent in-source fragmentation, and 82% of the peptides were identified with a mass measurement accuracy of less than 5 ppm. More than 75% of the identified proteins have at least 10 matched peptides, 88% of the identified proteins have greater than 30% of coverage, and 87% of the identified proteins occur in all four replicates. 78% of the identified proteins correspond to all glycinin and beta-conglycinin chains.The theoretical Uniprot peptide database has 723,749 entries, and 548,336 peptides have molecular weights of greater than 500 Da. Seed proteins represent 0.86% of the protein database entries. At the peptide level, trypsin-digested seed proteins represent only 0.3% of the theoretical Uniprot peptide database. A total of 22% of all database peptides have a pI value of less than 5, and 25% of them have a pI value between 5 and 8. Based on the detection range of typical NanoUPLC-MSE experiments, i.e., 500 to 5000 Da, 64 proteins will not be identified.

CONCLUSIONS

NanoUPLC-MSE experiments provide good protein coverage within a peptide error of 5 ppm and a wide MW detection range from 500 to 5000 Da. A second digestion enzyme should be used depending on the tissue or proteins to be analyzed. In the case of seed tissue, trypsin protein digestion results offer good databank coverage. The Uniprot database has many duplicate entries that may result in false protein homolog associations when using NanoUPLC-MSE analysis. The proteomic profile of the EMBRAPA BR-16 seed lacks certain described proteins relative to the profiles of transgenic soybeans reported in other works.

Mobilization of seed protein reserves

The mobilization of seed storage proteins upon seed imbibition and germination is a crucial process in the establishment of the seedling. Storage proteins fold compactly, presenting only a few vulnerable regions for initial proteolytic digestion. Evolutionarily related storage proteins have similar three-dimensional structure, and thus tend to be initially cleaved at similar sites. The initial cleavage makes possible subsequent rapid and extensive breakdown catalyzed by endo- and exopeptidases. The proteolytic enzymes that degrade the storage proteins during mobilization identified so far are mostly cysteine proteases, but also include serine, aspartic and metalloproteases. Plants often ensure early initiation of storage protein mobilization by depositing active proteases during seed maturation, in the very compartments where storage proteins are sequestered. Various means are used in such cases to prevent proteolytic attack until after imbibition of the seed with water. This constraint, however, is not always enforced as the dry seeds of some plant species contain proteolytic intermediates as a result of limited proteolysis of some storage proteins. Besides addressing fundamental questions in plant protein metabolism, studies of the mobilization of storage proteins will point out proteolytic events to avoid in large-scale production of cloned products in seeds. Conversely, proteolytic enzymes may be applied toward reduction of food allergens, many of which are seed storage proteins.

Detection and expression analysis of recombinant proteins in plant-derived complex mixtures using nanoUPLC-MS(E)

The use of mass spectrometry to identify recombinant proteins that are expressed in total soluble proteins (TSPs) from plant extracts is necessary to accelerate further processing steps. For example, the method consists of TSP sample preparation and trypsin digestion prior to the preliminary characterization using nanoUPLC-MS(E) analysis of the recombinant proteins that are expressed in TSP samples of transgenic soybean seeds. A TSP sample as small as 50 μg can be effectively analyzed. In this study, transgenic soybean seeds that expressed recombinant cancer testis antigen (CTAG) were used. The procedure covered 30% of the protein sequence and was quantified at 0.26 ng, which corresponded to 0.1% of the TSP sample. A comparative proteomic profile was generated by the comparison of a negative control and sample that showed a unique expression pattern of CTAG in a transgenic line. The experimental data from the TSP extraction, sample preparation and data analysis are discussed herein.

A minimal DNA cassette as a vector for genetic transformation of soybean (Glycine max)

Currently, the market demands products committed to protecting human health and the environment, known as clean products. We developed a protocol using DNA fragments containing only the gene sequence of interest, to replace the circular vectors containing genes for antibiotic resistance and other undesirable sequences, for obtaining transgenic soybeans for microparticle bombardment. Vector pAC321 was digested with the restriction enzyme PvuII to produce the 6159 bp ahas fragment, which contains the mutated ahas gene from Arabidopsis thaliana (Brassicaceae), under the control of its own promoter and terminator. This gene confers resistance against imazapyr, a herbicidal molecule of the imidazolinone class, capable of systemically translocating and concentrating in the apical meristematic region of the plant, the same region used for the introduction of the transgenes. This fragment was used to generate 10 putative transgenic soybean lines.