Production of a recombinant industrial protein using barley cell cultures

Disposable Bioreactors Used in Process Development and Production Processes with Plant Cell and Tissue Cultures

The bioreactor is the centerpiece of the upstream processing in any biotechnological production process. Its design, the cultivation parameters, the production cell line, and the culture medium all have a major influence on the efficiency of the process and the result of the cultivation. Disposable bioreactors have been used for the past 20 years, playing a major role in process development and commercial production of high-value substances at medium scales.Our review deals with scalable, disposable bioreactors that have proven to be useful for the cultivation of plant cell and tissue cultures. Based on the definitions of terms and a categorization approach, the most commonly used, commercially available, disposable bioreactor types are presented below. The focus is on wave-mixed, stirred, and orbitally shaken bioreactors. In addition to their instrumentation and bioengineering characteristics, cultivation results are discussed, and emerging trends for the development of disposable bioreactors for plant cell and tissue cultures are also addressed.

Green biomanufacturing in recombinant collagen biosynthesis: trends and selection in various expression systems

Collagen, classically derived from animal tissue, is an all-important protein material widely used in biomedical materials, cosmetics, fodder, food, etc. The production of recombinant collagen through different biological expression systems using bioengineering techniques has attracted significant interest in consideration of increasing market demand and the process complexity of extraction. Green biomanufacturing of recombinant collagen has become one of the focus topics. While the bioproduction of recombinant collagens (type I, II, III, etc.) has been commercialized in recent years, the biosynthesis of recombinant collagen is extremely challenging due to protein immunogenicity, yield, degradation, and other issues. The rapid development of synthetic biology allows us to perform a heterologous expression of proteins in diverse expression systems, thus optimizing the production and bioactivities of recombinant collagen. This review describes the research progress in the bioproduction of recombinant collagen over the past two decades, focusing on different expression systems (prokaryotic organisms, yeasts, plants, insects, mammalian and human cells, etc.). We also discuss the challenges and future trends in developing market-competitive recombinant collagens.

Optimising expression and extraction of recombinant proteins in plants

Recombinant proteins are of paramount importance for research, industrial and medical use. Numerous expression chassis are available for recombinant protein production, and while bacterial and mammalian cell cultures are the most widely used, recent developments have positioned transgenic plant chassis as viable and often preferential options. Plant chassis are easily maintained at low cost, are hugely scalable, and capable of producing large quantities of protein bearing complex post-translational modification. Several protein targets, including antibodies and vaccines against human disease, have been successfully produced in plants, highlighting the significant potential of plant chassis. The aim of this review is to act as a guide to producing recombinant protein in plants, discussing recent progress in the field and summarising the factors that must be considered when utilising plants as recombinant protein expression systems, with a focus on optimising recombinant protein expression at the genetic level, and the subsequent extraction and purification of target proteins, which can lead to substantial improvements in protein stability, yield and purity.

Long-Lasting Stable Expression of Human LL-37 Antimicrobial Peptide in Transgenic Barley Plants

Antimicrobial peptides play a crucial role in the innate immune system of multicellular organisms. LL-37 is the only known member of the human cathelicidin family. As well as possessing antibacterial properties, it is actively involved in various physiological responses in eukaryotic cells. Accordingly, there is considerable interest in large-scale, low-cost, and microbial endotoxin-free production of LL-37 recombinant peptides for pharmaceutical applications. As a heterologous expression biofactory, we have previously obtained homologous barley (Hordeum vulgare L.) as an attractive vehicle for producing recombinant human LL-37 in the grain storage compartment, endosperm. The long-term stability of expression and inheritance of transgenes is necessary for the successful commercialization of recombinant proteins. Here, we report the stable inheritance and expression of the LL-37 gene in barley after six generations, including two consecutive seasons of experimental field cultivation. The transgenic plants showed normal growth and remained fertile. Based on the bacteria viability test, the produced peptide LL-37 retained high antibacterial activity.

Three Decades of Research on Recombinant Collagens: Reinventing the Wheel or Developing New Biomedical Products?

Collagens provide the building blocks for diverse tissues and organs. Furthermore, these proteins act as signaling molecules that control cell behavior during organ development, growth, and repair. Their long half-life, mechanical strength, ability to assemble into fibrils and networks, biocompatibility, and abundance from readily available discarded animal tissues make collagens an attractive material in biomedicine, drug and food industries, and cosmetic products. About three decades ago, pioneering experiments led to recombinant human collagens' expression, thereby initiating studies on the potential use of these proteins as substitutes for the animal-derived collagens. Since then, scientists have utilized various systems to produce native-like recombinant collagens and their fragments. They also tested these collagens as materials to repair tissues, deliver drugs, and serve as therapeutics. Although many tests demonstrated that recombinant collagens perform as well as their native counterparts, the recombinant collagen technology has not yet been adopted by the biomedical, pharmaceutical, or food industry. This paper highlights recent technologies to produce and utilize recombinant collagens, and it contemplates their prospects and limitations.

Advances in Plant-Derived Scaffold Proteins

Scaffold proteins form critical biomatrices that support cell adhesion and proliferation for regenerative medicine and drug screening. The increasing demand for such applications urges solutions for cost effective and sustainable supplies of hypoallergenic and biocompatible scaffold proteins. Here, we summarize recent efforts in obtaining plant-derived biosynthetic spider silk analogue and the extracellular matrix protein, collagen. Both proteins are composed of a large number of tandem block repeats, which makes production in bacterial hosts challenging. Furthermore, post-translational modification of collagen is essential for its function which requires co-transformation of multiple copies of human prolyl 4-hydroxylase. We discuss our perspectives on how the GAANTRY system could potentially assist the production of native-sized spider dragline silk proteins and prolyl hydroxylated collagen. The potential of recombinant scaffold proteins in drug delivery and drug discovery is also addressed.

Molecular Farming in Barley: Development of a Novel Production Platform to Produce Human Antimicrobial Peptide LL-37

The peptide LL-37, a component of the human innate immune system, represents a promising drug candidate. In particular, the development of low-cost production platform technology is a critical bottleneck in its use in medicine. In the present study, a viable approach for the LL-37 production in transgenic barley is developed. First, comparative analyses of the effects of different fused peptide epitope tags applicable for accumulation and purification on LL-37 production yield are performed using transient expression in tobacco leaves. Following the selection of the most yielding fusion peptide strategies, eight different constructs for the expression of codon optimized chimeric LL-37 genes in transgenic barley plants are created. The expression of individual constructs is driven either by an endosperm-specific promoter of the barley B1 hordein gene or by the maize ubiquitin promoter. The transgenes are stably integrated into the barley genome and inherited in the subsequent generation. All transgenic lines show normal phenotypes and are fertile. LL-37 accumulated in the barley seeds up to 0.55 mg per 1 kg of grain. The fused epitope tags are cleaved off by the use of enterokinase. Furthermore, in planta produced LL-37 including the fused versions is biologically active.

Variability in the production of tannins and other polyphenols in cell cultures of 12 Nordic plant species

The polyphenol profiles of 18 cell cultures from 12 plant species were screened. The detected polyphenol fingerprints were diverse and differed from polyphenol profiles typically found in corresponding plant species. Cell cultures originating from 12 different plant species growing or grown in the Nordic countries were screened for their ability to synthesize polyphenols to assess their suitability for future studies and applications. The focus was on plant families Rosaceae and Ericaceae. On average, the Rosaceae cultures were the most efficient to produce hydrolysable tannins and the Ericaceae cultures were the most efficient to produce proanthocyanidins. This is in line with the general trend of polyphenols found in Rosaceae and Ericaceae leaves and fruits, even though several individual cell cultures differed from natural plants in their polyphenolic composition. Overall, several of the studied cell cultures exhibited capability in producing a large variety of polyphenols, including tannins with a high molecular weight, thus also showing promise for further studies concerning, for example, the accumulation of specific polyphenols or biosynthesis of polyphenols in the cell cultures.

Adding Functions to Biomaterial Surfaces through Protein Incorporation

The concept of biomaterials has evolved from one of inert mechanical supports with a long-term, biologically inactive role in the body into complex matrices that exhibit selective cell binding, promote proliferation and matrix production, and may ultimately become replaced by newly generated tissues in vivo. Functionalization of material surfaces with biomolecules is critical to their ability to evade immunorecognition, interact productively with surrounding tissues and extracellular matrix, and avoid bacterial colonization. Antibody molecules and their derived fragments are commonly immobilized on materials to mediate coating with specific cell types in fields such as stent endothelialization and drug delivery. The incorporation of growth factors into biomaterials has found application in promoting and accelerating bone formation in osteogenerative and related applications. Peptides and extracellular matrix proteins can impart biomolecule- and cell-specificities to materials while antimicrobial peptides have found roles in preventing biofilm formation on devices and implants. In this progress report, we detail developments in the use of diverse proteins and peptides to modify the surfaces of hard biomaterials in vivo and in vitro. Chemical approaches to immobilizing active biomolecules are presented, as well as platform technologies for isolation or generation of natural or synthetic molecules suitable for biomaterial functionalization.

Plant-based biopharming of recombinant human lactoferrin

Recombinant proteins are currently recognized as pharmaceuticals, enzymes, food constituents, nutritional additives, antibodies and other valuable products for industry, healthcare, research, and everyday life. Lactoferrin (Lf), one of the promising human milk proteins, occupies the expanding biotechnological food market niche due to its important versatile properties. Lf shows antiviral, antimicrobial, antiprotozoal and antioxidant activities, modulates cell growth rate, binds glycosaminoglycans and lipopolysaccharides, and also inputs into the innate/specific immune responses. Development of highly efficient human recombinant Lf expression systems employing yeasts, filamentous fungi and undoubtedly higher plants as bioreactors for the large-scale Lf production is a biotechnological challenge. This review highlights the advantages and disadvantages of the existing non-animal Lf expression systems from the standpoint of protein yield and its biological activity. Special emphasis is put on the benefits of monocot plant system for Lf expression and the biosafety aspects of the transgenic Lf-expressing plants.

Recombinant barley-produced antibody for detection and immunoprecipitation of the major bovine milk allergen, β-lactoglobulin

Recombinant allergens and antibodies are needed for diagnostic, therapeutic, food processing and quality verification purposes. The aim of this work was to develop a barley-based production system for β-lactoglobulin (BLG) specific immunoglobulin E antibody (D1 scFv). The expression level in the best barley cell clone was 0.8-1.2 mg/kg fresh weight, and was constant over an expression period of 21 days. In the case of barley grains, the highest stable productivity (followed up to T2 grains) was obtained when the D1 scFv cDNA was expressed under a seed-specific Glutelin promoter rather than under the constitutive Ubiquitin promoter. Translational fusion of ER retention signal significantly improved the accumulation of recombinant antibody. Furthermore, lines without ER retention signal lost D1 scFv accumulation in T2 grains. Pilot scale purification was performed for a T2 grain pool (51 g) containing 55.0 mg D1 scFv/kg grains. The crude extract was purified by a two-step purification protocol including IMAC and size exclusion chromatography. The purification resulted in a yield of 0.47 mg of D1 scFv (31 kD) with high purity. Enzyme-linked immunosorbent assay revealed that 29 % of the purified protein was fully functional. In immunoprecipitation assay the purified D1 scFv recognized the native 18 kD BLG in the milk sample. No binding was observed with the heat-treated milk sample, as expected. The developed barley-based expression system clearly demonstrated its potential for application in the processing of dairy milk products as well as in detecting allergens from foods possibly contaminated by bovine milk.

Transgenic barley: a prospective tool for biotechnology and agriculture

Barley (Hordeum vulgare L.) is one of the founder crops of agriculture, and today it is the fourth most important cereal grain worldwide. Barley is used as malt in brewing and distilling industry, as an additive for animal feed, and as a component of various food and bread for human consumption. Progress in stable genetic transformation of barley ensures a potential for improvement of its agronomic performance or use of barley in various biotechnological and industrial applications. Recently, barley grain has been successfully used in molecular farming as a promising bioreactor adapted for production of human therapeutic proteins or animal vaccines. In addition to development of reliable transformation technologies, an extensive amount of various barley genetic resources and tools such as sequence data, microarrays, genetic maps, and databases has been generated. Current status on barley transformation technologies including gene transfer techniques, targets, and progeny stabilization, recent trials for improvement of agricultural traits and performance of barley, especially in relation to increased biotic and abiotic stress tolerance, and potential use of barley grain as a protein production platform have been reviewed in this study. Overall, barley represents a promising tool for both agricultural and biotechnological transgenic approaches, and is considered an ancient but rediscovered crop as a model industrial platform for molecular farming.

Hosting the plant cells in vitro: recent trends in bioreactors

Biotechnological production of high-value metabolites and therapeutic proteins by plant in vitro systems has been considered as an attractive alternative of classical technologies. Numerous proof-of-concept studies have illustrated the feasibility of scaling up plant in vitro system-based processes while keeping their biosynthetic potential. Moreover, several commercial processes have been established so far. Though the progress on the field is still limited, in the recent years several bioreactor configurations has been developed (e.g., so-called single-use bioreactors) and successfully adapted for growing plant cells in vitro. This review highlights recent progress and limitations in the bioreactors for plant cells and outlines future perspectives for wider industrialization of plant in vitro systems as "green cell factories" for sustainable production of value-added molecules.

Optimization of multiple shoot induction and plant regeneration in Indian barley (Hordeum vulgare) cultivars using mature embryos

Barley is the fourth most important crop in the world. Development of a regeneration system using immature embryos is both time consuming and laborious. The present study was initiated with a view to develop a regeneration system in six genotypes of Indian barley (Hordeum vulgare) cultivars as a prerequisite to transformation. The mature embryos were excised from seeds and cultured on MS medium supplemented with high and low concentrations of cytokinins and auxins respectively. The MS medium containing 3 mg/L N(6)-benzylaminopurine (BA) and 0.5 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) was found to be the most effective for multiple shoot formation in HOR7231 cultivar that could produce 12 shoots per explant. The other cultivars HOR4409 and HOR3844 produced a minimum number of adventitious shoots (1.33 and 1.67 respectively) on MS medium supplemented with 1 mg/L BA and 0.3 mg/L 2,4-D. The elongated shoots were separated and successfully rooted on MS medium containing 1 mg/L indole-3-acetic acid (IAA). The response of different barley cultivars was found to be varying with respect to multiple shoot production. This is the first report of multiple shoot induction and plantlet regeneration in Indian cultivar of barley which would be useful for genetic transformation.

Unusual biophysics of intrinsically disordered proteins

Research of a past decade and a half leaves no doubt that complete understanding of protein functionality requires close consideration of the fact that many functional proteins do not have well-folded structures. These intrinsically disordered proteins (IDPs) and proteins with intrinsically disordered protein regions (IDPRs) are highly abundant in nature and play a number of crucial roles in a living cell. Their functions, which are typically associated with a wide range of intermolecular interactions where IDPs possess remarkable binding promiscuity, complement functional repertoire of ordered proteins. All this requires a close attention to the peculiarities of biophysics of these proteins. In this review, some key biophysical features of IDPs are covered. In addition to the peculiar sequence characteristics of IDPs these biophysical features include sequential, structural, and spatiotemporal heterogeneity of IDPs; their rough and relatively flat energy landscapes; their ability to undergo both induced folding and induced unfolding; the ability to interact specifically with structurally unrelated partners; the ability to gain different structures at binding to different partners; and the ability to keep essential amount of disorder even in the bound form. IDPs are also characterized by the "turned-out" response to the changes in their environment, where they gain some structure under conditions resulting in denaturation or even unfolding of ordered proteins. It is proposed that the heterogeneous spatiotemporal structure of IDPs/IDPRs can be described as a set of foldons, inducible foldons, semi-foldons, non-foldons, and unfoldons. They may lose their function when folded, and activation of some IDPs is associated with the awaking of the dormant disorder. It is possible that IDPs represent the "edge of chaos" systems which operate in a region between order and complete randomness or chaos, where the complexity is maximal. This article is part of a Special Issue entitled: The emerging dynamic view of proteins: Protein plasticity in allostery, evolution and self-assembly.

[Current status in the commercialization and application of genetically modified plants and their effects on human and livestock health and phytoremediation]

Developments in the use of genetically modified plants for human and livestock health and phytoremediation were surveyed using information retrieved from Entrez PubMed, Chemical Abstracts Service, Google, congress abstracts and proceedings of related scientific societies, scientific journals, etc. Information obtained was classified into 8 categories according to the research objective and the usage of the transgenic plants as 1: nutraceuticals (functional foods), 2: oral vaccines, 3: edible curatives, 4: vaccine antigens, 5: therapeutic antibodies, 6: curatives, 7: diagnostic agents and reagents, and 8: phytoremediation. In total, 405 cases were collected from 2006 to 2010. The numbers of cases were 120 for nutraceuticals, 65 for oral vaccines, 25 for edible curatives, 36 for vaccine antigens, 36 for therapeutic antibodies, 76 for curatives, 15 for diagnostic agents and reagents, and 40 for phytoremediation (sum of each cases was 413 because some reports were related to several categories). Nutraceuticals, oral vaccines and curatives were predominant. The most frequently used edible crop was rice (51 cases), and tomato (28 cases), lettuce (22 cases), potato (18 cases), corn (15 cases) followed.

Bioreactor systems for in vitro production of foreign proteins using plant cell cultures

Plant cells have been demonstrated to be an attractive heterologous expression host (using whole plants and in vitro plant cell cultures) for foreign protein production in the past 20years. In recent years in vitro liquid cultures of plant cells in a fully contained bioreactor have become promising alternatives to traditional microbial fermentation and mammalian cell cultures as a foreign protein expression platform, due to the unique features of plant cells as a production host including product safety, cost-effective biomanufacturing, and the capacity for complex protein post-translational modifications. Heterologous proteins such as therapeutics, antibodies, vaccines and enzymes for pharmaceutical and industrial applications have been successfully expressed in plant cell culture-based bioreactor systems including suspended dedifferentiated plant cells, moss, and hairy roots, etc. In this article, the current status and emerging trends of plant cell culture for in vitro production of foreign proteins will be discussed with emphasis on the technological progress that has been made in plant cell culture bioreactor systems.

Post-translational modification of plant-made foreign proteins; glycosylation and beyond

The complex and diverse nature of the post-translational modification (PTM) of proteins represents an efficient and cost-effective mechanism for the exponential diversification of the genome. PTMs have been shown to affect almost every aspect of protein activity, including function, localisation, stability, and dynamic interactions with other molecules. Although many PTMs are evolutionarily conserved there are also important kingdom-specific modifications which should be considered when expressing recombinant proteins. Plants are gaining increasing acceptance as an expression system for recombinant proteins, particularly where eukaryotic-like PTMs are required. Glycosylation is the most extensively studied PTM of plant-made recombinant proteins. However, other types of protein processing and modification also occur which are important for the production of high quality recombinant protein, such as hydroxylation and lipidation. Plant and/or protein engineering approaches offer many opportunities to exploit PTM pathways allowing the molecular farmer to produce a humanised product with modifications functionally similar or identical to the native protein. Indeed, plants have demonstrated a high degree of tolerance to changes in PTM pathways allowing recombinant proteins to be modified in a specific and controlled manner, frequently resulting in a homogeneity of product which is currently unrivalled by alternative expression platforms. Whether a recombinant protein is intended for use as a scientific reagent, a cosmetic additive or as a pharmaceutical, PTMs through their presence and complexity, offer an extensive range of options for the rational design of humanised (biosimilar), enhanced (biobetter) or novel products.

Hydroxylation of recombinant human collagen type I alpha 1 in transgenic maize co-expressed with a recombinant human prolyl 4-hydroxylase

Background

Collagens require the hydroxylation of proline (Pro) residues in their triple-helical domain repeating sequence Xaa-Pro-Gly to function properly as a main structural component of the extracellular matrix in animals at physiologically relevant conditions. The regioselective proline hydroxylation is catalyzed by a specific prolyl 4-hydroxylase (P4H) as a posttranslational processing step.

Results

A recombinant human collagen type I α-1 (rCIα1) with high percentage of hydroxylated prolines (Hyp) was produced in transgenic maize seeds when co-expressed with both the α- and β- subunits of a recombinant human P4H (rP4H). Germ-specific expression of rCIα1 using maize globulin-1 gene promoter resulted in an average yield of 12 mg/kg seed for the full-length rCIα1 in seeds without co-expression of rP4H and 4 mg/kg seed for the rCIα1 (rCIα1-OH) in seeds with co-expression of rP4H. High-resolution mass spectrometry (HRMS) analysis revealed that nearly half of the collagenous repeating triplets in rCIα1 isolated from rP4H co-expressing maize line had the Pro residues changed to Hyp residues. The HRMS analysis determined the Hyp content of maize-derived rCIα1-OH as 18.11%, which is comparable to the Hyp level of yeast-derived rCIα1-OH (17.47%) and the native human CIa1 (14.59%), respectively. The increased Hyp percentage was correlated with a markedly enhanced thermal stability of maize-derived rCIα1-OH when compared to the non-hydroxylated rCIα1.

Conclusions

This work shows that maize has potential to produce adequately modified exogenous proteins with mammalian-like post-translational modifications that may be require for their use as pharmaceutical and industrial products.

Transgene expression systems in the Triticeae cereals

The control of transgene expression is vital both for the elucidation of gene function and for the engineering of transgenic crops. Given the dominance of the Triticeae cereals in the agricultural economy of the temperate world, the development of well-performing transgene expression systems of known functionality is of primary importance. Transgenes can be expressed either transiently or stably. Transient expression systems based on direct or virus-mediated gene transfer are particularly useful in situations where the need is to rapidly screen large numbers of genes. However, an unequivocal understanding of gene function generally requires that a transgene functions throughout the plant's life and is transmitted through the sexual cycle, since this alone allows its effect to be decoupled from the plant's response to the generally stressful gene transfer event. Temporal, spatial and quantitative control of a transgene's expression depends on its regulatory environment, which includes both its promoter and certain associated untranslated region sequences. While many transgenic approaches aim to manipulate plant phenotype via ectopic gene expression, a transgene sequence can be also configured to down-regulate the expression of its endogenous counterpart, a strategy which exploits the natural gene silencing machinery of plants. In this review, current technical opportunities for controlling transgene expression in the Triticeae species are described. Apart from protocols for transient and stable gene transfer, the choice of promoters and other untranslated regulatory elements, we also consider signal peptides, as they too govern the abundance and particularly the sub-cellular localization of transgene products.

High cell density cultivation and recombinant protein production with Escherichia coli in a rocking-motion-type bioreactor

Background

Single-use rocking-motion-type bag bioreactors provide advantages compared to standard stirred tank bioreactors by decreased contamination risks, reduction of cleaning and sterilization time, lower investment costs, and simple and cheaper validation. Currently, they are widely used for cell cultures although their use for small and medium scale production of recombinant proteins with microbial hosts might be very attractive. However, the utilization of rocking- or wave-induced motion-type bioreactors for fast growing aerobic microbes is limited because of their lower oxygen mass transfer rate. A conventional approach to reduce the oxygen demand of a culture is the fed-batch technology. New developments, such as the BIOSTAT^® CultiBag RM system pave the way for applying advanced fed-batch control strategies also in rocking-motion-type bioreactors. Alternatively, internal substrate delivery systems such as EnBase^® Flo provide an opportunity for adopting simple to use fed-batch-type strategies to shaken cultures. Here, we investigate the possibilities which both strategies offer in view of high cell density cultivation of E. coli and recombinant protein production.

Results

Cultivation of E. coli in the BIOSTAT^® CultiBag RM system in a conventional batch mode without control yielded an optical density (OD₆₀₀) of 3 to 4 which is comparable to shake flasks. The culture runs into oxygen limitation. In a glucose limited fed-batch culture with an exponential feed and oxygen pulsing, the culture grew fully aerobically to an OD₆₀₀ of 60 (20 g L^-1 cell dry weight). By the use of an internal controlled glucose delivery system, EnBase^® Flo, OD₆₀₀ of 30 (10 g L^-1 cell dry weight) is obtained without the demand of computer controlled external nutrient supply. EnBase^® Flo also worked well in the CultiBag RM system with a recombinant E. coli RB791 strain expressing a heterologous alcohol dehydrogenase (ADH) to very high levels, indicating that the enzyme based feed supply strategy functions well for recombinant protein production also in a rocking-motion-type bioreactor.

Conclusions

Rocking-motion-type bioreactors may provide an interesting alternative to standard cultivation in bioreactors for cultivation of bacteria and recombinant protein production. The BIOSTAT^® Cultibag RM system with the single-use sensors and advanced control system paves the way for the fed-batch technology also to rocking-motion-type bioreactors. It is possible to reach cell densities which are far above shake flasks and typical for stirred tank reactors with the improved oxygen transfer rate. For more simple applications the EnBase^® Flo method offers an easy and robust solution for rocking-motion-systems which do not have such advanced control possibilities.

Purification and characterization of a transgenic corn grain-derived recombinant collagen type I alpha 1

Corn offers advantages as a transgenic host for producing recombinant proteins required at large volumes (1,000's of tons per year) and low cost (less than US$50/kg) by generating them as co-products of biorefining. We describe the purification and characterization of a corn grain-derived mammalian structural protein having such market characteristics: a full length recombinant collagen type I alpha 1 (rCI alpha 1) chain. Material properties of interest are gelation behavior, which would depend on as yet unverified ability of corn to carry out post-translational prolyl hydroxylation and formation of triple helical conformation. The starting material was grain where the expression of rCI alpha 1 had been directed by an embryo-specific promoter. Purification consisted of extraction at low pH followed by membrane and chromatographic steps to isolate rCI alpha 1 for characterization. The amino acid composition and immunoreactivity of CI alpha 1 was similar to that of an analogous native human CI alpha 1 and to rCI alpha 1 produced by the yeast Pichia pastoris. Tandem mass spectrometry confirmed the primary sequence of the corn-derived rCI alpha 1 with 46% coverage. Fragments of the rCI alpha 1 chains were also observed, possibly caused by endogenous plant proteases. The corn-derived rCI alpha 1 had a low level of prolyl hydroxylation (approximately 1% versus 11%) relative to animal-derived CI alpha 1 and folded into its characteristic triple-helical structure as indicated by its resistance to pepsin digestion below its melting temperature of 26(o)C. The 29 amino acid foldon fused to the C-terminus to initiate triple helix formation was not cleaved from the rCI alpha 1 chains, but could be removed by pepsin treatment.

Production of bioactive, post-translationally modified, heterotrimeric, human recombinant type-I collagen in transgenic tobacco

Collagen's biocompatibility, biodegradability and low immunogenicity render it advantageous for extensive application in pharmaceutical or biotechnological disciplines. However, typical collagen extraction from animal or cadaver sources harbors risks including allergenicity and potential sample contamination with pathogens. In this work, two human genes encoding recombinant heterotrimeric collagen type I (rhCOL1) were successfully coexpressed in tobacco plants with the human prolyl-4-hydroxylase (P4H) and lysyl hydroxylase 3 (LH3) enzymes, responsible for key posttranslational modifications of collagen. Plants coexpressing all five vacuole-targeted proteins generated intact procollagen yields of approximately 2% of the extracted total soluble proteins. Plant-extracted rhCOL1 formed thermally stable triple helical structures and demonstrated biofunctionality similar to human tissue-derived collagen supporting binding and proliferation of adult peripheral blood-derived endothelial progenitor-like cells. Through a simple, safe and scalable method of rhCOL1 production and purification from tobacco plants, this work broadens the potential applications of human recombinant collagen in regenerative medicine.

Production of a recombinant full-length collagen type I alpha-1 and of a 45-kDa collagen type I alpha-1 fragment in barley seeds

Recombinant DNA technology can be used to design and express collagen and gelatin-related proteins with predetermined composition and structure. Barley seed was chosen as a production host for a recombinant full-length collagen type I alpha1 (rCIa1) and a related 45-kDa rCIa1 fragment. The transgenic barley seeds were shown to accumulate both the rCIa1 and the 45-kDa rCIa1 fragment. Even when the amount of the rCIa1 was just above the detection threshold, this work using rCIa1 as a model demonstrated for the first time that barley seed can be used as a production system for collagen-related structural proteins. The 45-kDa rCI1a fragment expression, targeted to the endoplasmic reticulum, was controlled by three different promoters (a constitutive maize ubiquitin, seed endosperm-specific rice glutelin and germination-specific barley alpha-amylase fusion) to compare their effects on rCIa1 accumulation. Highest accumulation of the 45-kDa rCIa1 was obtained with the glutelin promoter (140 mg/kg seed), whereas the lowest accumulation was obtained with the alpha-amylase promoter. To induce homozygosity for stable 45-kDa rCIa1 production in the transgenic lines, doubled haploid (DH) progeny was generated through microspore culture. The 45-kDa rCIa1 expression levels achieved from the best DH lines were 13 mg/kg dry seeds under the ubiquitin promoter and 45 mg/kg dry seeds under the glutelin promoter. Mass spectroscopy and amino acid composition analysis of the purified 45-kDa rCIa1 fragment revealed that a small percent of prolines were hydroxylated with no additional detectable post-translational modifications.