Proteins secretion

Yeast. The advantages of expression in yeast include potentially high level production of proteins, the abiUty to have expressed proteins secreted into the media for ease of purification, and relatively low cost, easy scale-up. A disadvantage is that plasmid instabiUty may be a problem which can lead to low product yield. Whereas post-translational modification occurs in yeast, proteins are quite often hyperglycosylated. This is generally a problem with expression in Saccharomyces cerevisiae but not for the more recently used yeast host Pichiapastoris (25) (see Yeasts). 

In 1929, Castie (7) tied the work of Combe and Addison with that of Whipple, Miaot, and Murphy by ptoposiag that both an extrinsic factor and an intrinsic factor ate iavolved ia the coatrol of pernicious anemia. The extrinsic factor, from food, is vitamin 2- Th intrinsic factor is a specific B22-biading protein secreted by the stomach. This protein is requited for vitamin B 2 absorption. 

The term adipokine refers to any protein secreted from adipocytes [1]. Collectively, the various adipokines form the adipokinome which together with the lipid moieties secreted from fat cells (e.g. fatty acids, cholesterol, retinol) constitute what can be referred to as the secretome of adipocytes. Most adipokines are also secreted from other cell types in other organs, but one in particular - adiponectin - is considered to be exclusive to adipocytes. 

Chemokines are a family of small cytokines, or proteins secreted by cells. Proteins are classified as chemokines according to shared structural characteristics such as small size (8-10 kDa in size), and the presence of four... 

Similarly, in developing Drosophila the response to wg is influenced by the relative abundance and ligand affinity of receptors expressed in the target tissue. A synthesis of the available data from all species suggests that the response to a specific Wnt signal in vivo is influenced both by the particular Wnt protein secreted and by the receptors and other downstream molecules present in the target tissue. 

Each deposited volume contains all of the proteins secreted by 5. 10 cells. 

SDS gel electrophoresis separation in total denaturing conditions was carried out on the protein of culture filtrates and proteins of known molecular mass. The four dark bands (Figure 2) which appear in the gel between 45 and 36 kDa of the standards were assumed to be PG based on the gel filtration results for PG activity and total protein. The relative molecular mass of the four protein bands were estimated as 45 kDa, 42 kDa, 39 kDa and 36 kDa. It was calculated that about 85% of total protein secreted into the culture medium by K. marxianus consisted of PG. 

Cytokines, proteins secreted by cells, serve as intercellular mediators (see Table 54—1). An imbalance of proinflammatory... 

Achen, M. G., et al. (1992). Protein synthesis at the blood-brain barrier. The major protein secreted by amphibian choroid plexus is a lipocalin. J. Biol. Chem. 267, 23170-4. 

On a laboratory scale, the most commonly used E. coli strains are BL21 (protease deficient) and K12 (seems to show enhanced disulfide bond formation) and some optimized derivatives [13] for example, C41 and C43 for membrane proteins expression, Rosetta strains and BL21 CodonPlus strains with overexpressed tRNAs to deal with rare E. coli codons, or JM 83 for proteins secreted into the periplasm. Strains and plasmids are commercially available and were reviewed in several papers [13,26],... 

Sims, A.H., Gent, M.E., Lanthaler, K. et al. (2005) Transcriptome analysis of recombinant protein secretion by Aspergillus nidulans and the unfolded-protein response in vivo. Applied and Environmental Microbiology, 71 (5), 2737-2747. 

Iwashita, K. (2002) Recent studies of protein secretion by filamentous fungi. Journal of Bioscience and Bioengineering, 94 (6), 530-535. 

As indicated in Table 2.1, most of the promoters used in plant tissue culture have been based on the constitutive cauliflower mosaic virus (CaMV) 35S promoter. In contrast, inducible promoters have the advantage of allowing foreign proteins to be expressed at a time that is most conducive to protein accumulation and stability. Although a considerable number of inducible promoters has been developed and used in plant culture applications, e.g. [32-37], the only one to be applied thus far for the production of biopharmaceutical proteins is the rice a-amylase promoter. This promoter controls the production of an a-amylase isozyme that is one of the most abundant proteins secreted from cultured rice cells after sucrose starvation. The rice a-amylase promoter has been used for expression of hGM-CSF [10], aranti-trypsin [12, 29, 38, 39] and human lysozyme [30]. 

Alterations to the proteins and pre-proteins expressed by cultured plant cells have been used to facilitate product recovery. A leader sequence is required for foreign protein secretion from plant cells into the apoplast and then into the culture medium. As indicated in Table 2.1, plant, mammalian and viral sequences have been employed to achieve the entry of transgenic proteins into the bulk-flow pathway in plant cultures. 

Proteins produced in plant cells can remain within the cell or are secreted into the apoplast via the bulk transport (secretory) pathway. In whole plants, because levels of protein accumulated intracellularly, e. g. using the KDEL sequence to ensure retention in the endoplasmic reticulum, are often higher than when the product is secreted [58], foreign proteins are generally not directed for secretion. However, as protein purification from plant biomass is potentially much more difficult and expensive than protein recovery from culture medium, protein secretion is considered an advantage in tissue culture systems. For economic harvesting from the medium, the protein should be stable once secreted and should accumulate to high levels in the extracellular environment. 

The simplicity of plant culture media is considered an advantage for foreign protein production in tissue culture systems. However, as a mixture of salts and sugar containing several heavy metals but negligible protein (except for any protein secreted... 

---