Recombinant proteins expression in plants

Within each species, individual promoters resulted in distinct, tissue-dependent accumulation patterns. The cauliflower mosaic virus (CaMV) 35S promoter, for example, led to high-level accumulation in callus and leaves whereas the maize ubiqui-tin-1 promoter was the best choice for producing recombinant proteins in cereal seeds even though it is not in itself seed-specific [23]. The lack of such comparative studies for proteins other than rAbs makes it difficult to generalize an optimal expression strategy for all proteins. Tables 7.1 and 7.2 list recombinant proteins expressed in plants and provide details of the production system, promoters and other regulatory elements used in each case. 

Four basic strategies for recombinant protein expression in plants are transient expression, stable nuclear transformed plants, chloroplast transformed plants, and suspension cultures derived from stable transgenic lines. 

Engineering Glycosylation of Recombinant Proteins Expressed in Plants... 

There are additional means by which to develop plant varieties with enhanced nutritional functions. For example, recombinant antibodies expressed in plants can be used to inactivate or sequester specific host proteins or... 

The first successful therapeutic protein made in a transgenic system was human tissue plasminogen activator regulated by a milk-directed promoter for accumulation in mouse milk [5]. Human growth hormone, which was one of the first proteins produced using recombinant microbial systems in the early 1980s, became the first human protein expressed in plants (tobacco cells) in 1986 [6]. Since then, over 200 biotherapeutics of diverse origin. 

Knablein J, McCaman M. Modern Biopharmaceuticals - Recombinant Protein Expression in Transgenic Plants. Screening. Trends Drug Discov., 2003 6 33-35. 

A relatively small number of biotechnology companies operate in the field of recombinant proteins production in plants (Table 6.4). This small number represents roughly one-third of approximately 60 dedicated plant biotechnology companies - an unfavorable comparison to the several hundred small and medium-sized businesses that use bacterial, yeast or animal-based expression platforms and operate in the sector of red biotechnology. The number of plant-made recombinant proteins that have reached the market is also very limited, but has a healthy tendency to grow. 

The first recombinant protein expressed in cultured plant cells was human serum albumin, produced in tobacco suspension... 

Table 9.1 Recombinant proteins expressed in cultured plant cells...

Knablein, J., McCaman, M. 2003. Modem biopharmaceuticals — recombinant protein expression in transgenic plants. Screening Trends Drug Discov 6, 33—35. 

Yeast is the third expression system used to produce biopharmaceuticals. As mammalian systems, they possess the ability to cany out post-translational modifications of proteins, although the glycosylation pattern usually varies somewhat from the patterns observed on the native protein or on the protein expressed in mammalian cells. Two recombinant proteins expressed in Saccharomyces cerevisiae are now approved for general medical use hepatitis B surface antigen vaccine and the anticoagulant Hirudin . Alternative promising production systems, in particular transgenic animal and plant systems, are still in development but these systems have to prove that they are technically and economically attractive. 

Protein modification by glycosylation is found in all higher eukaryotes and plant proteins contain N-linllinked glycans. Variations between the glycans associated with native proteins and recombinant forms may complicate immunotherapy, whatever the heterologous expression system, and this is not a problem that is specific to recombinant proteins produced in plants. However, it is important to rmderstand the differences between plant and mammalian glycans in order to evalirate their relative importance. 

In this volume not all stress types are treated. Various aspects have been reviewed recently by various authors e.g. The effects of oxygen on recombinant protein expression by Konz et al. [2]. The Mechanisms by which bacterial cells respond to pH was considered in a Symposium in 1999 [3] and solvent effects were reviewed by de Bont in the article Solvent-tolerant bacteria in biocatalysis [4]. Therefore, these aspects are not considered in this volume. Influence of fluid dynamical stresses on micro-organism, animal and plant cells are in center of interest in this volume. In chapter 2, H.-J. Henzler discusses the quantitative evaluation of fluid dynamical stresses in various type of reactors with different methods based on investigations performed on laboratory an pilot plant scales. S. S. Yim and A. Shamlou give a general review on the effects of fluid dynamical and mechanical stresses on micro-organisms and bio-polymers in chapter 3. G. Ketzmer describes the effects of shear stress on adherent cells in chapter 4. Finally, in chapter 5, P. Kieran considers the influence of stress on plant cells. 

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