Proteins expression system for

Protein Expression, Systems for Solubilize Membrane Proteins, Techniques to... 

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Yokoyama S (2003) Protein expression systems for structural genomics and proteomics. Curr Opin Chem Biol 7 39-43... 

Terpe, K. (2006) Overview of bacterial expression systems for heterologous protein production from molecular and biochemical fundamentals to commercial systems. Applied Microbiology and Biotechnology, 72 (2), 211-222. 

Gamier, A., Cote, J., Nadeau, I. et al. (1994) Scale-up of the adenovirus expression system for the production of recombinant protein in human 293S cells. Cytotechnology, 15 (1-3), 145-155. 

Compared with whole plants, there has been limited development of foreign protein expression systems specifically for use in tissue culture. Some modifications of expression constructs have resulted in improved protein accumulation or have allowed simplified protein recovery. However, in general, modified expression systems have been tested only in a restricted number of cases and have not resulted in the large increases in product yield required for plant cultures to compete with other foreign protein production vehicles. Transient expression techniques, for example using viral vectors, that have been developed for use in whole plants have not yet been applied in plant tissue culture. 

Tab. 1.3 Application of expression systems for mammalian membrane proteins...

Other cell lines used in permeability studies include the T84 human colonic adenocarcinoma colonic crypt cell model. This line has a reduced carrier expression, secrets mucus, and has very high resistance [31, 32], The IEC cell line is a rat fetal intestinal epithelium cell with higher permeabilities than Caco-2 cells [33], LLC PKi is a pig kidney epithelial cell line with low expression of efflux systems, but expression systems for transport proteins [32], 2/4/A1 cells are a conditionally immortalized rat fetal intestinal epithelium line with crypt cell-like morphology and temperature-sensitive differentiation [34], They form differentiated monolayers with tight junctions, increased brush border enzymes when grown on extracellular matrices with laminin. Transport of drugs with LP in 2/4/A1 monolayers was comparable to that in the human jejunum and up to 300 times faster than that in Caco-2 monolayers. In contrast, the permeability of HP drugs was comparable in both cell lines [34],... 

Antibody coverage of the human proteome is estimated to be about 5 to 10% of all human proteins and isoforms (Valle and Jendoubi, 2003). A major bottleneck in the use of protein expression arrays is the lack of such a comprehensive set of these capture agents (Hanash, 2003). Since an equivalent of the polymerase chain reaction (PCR) process for mass amplification of low abxmdant proteins does not exist, the remaining library of proteome capture ligands will need to be generated by other means such as recombinant protein expression systems (Cahill, 2001). 

Optimization of gene expression may be applied at every step of the process, from initial cloning and characterization to initiation of clinical trials. Often several rounds of optimization will be required to select the expression system that produces the highest yield with the lowest cost fermentation and purification schemes. Significant resources are allocated for optimization because the best protein expression system can lead to several hundred- to a thousandfold increased efficiency in protein produced. Under these conditions, as much as 10% of total proteins produced by the expression system are target proteins. 

The first transient expression system for cytochrome P450 expression was the COS cell system which couples monkey cells with an SV40-based expression vector (Zuber et al., 1986). The cDNA of interest is introduced into a plasmid expression vector under control of a heterologous promoter. The vector is introduced into COS cells via electroporation or another method allowing DNA uptake. The plasmid vector replicates within the cells and cDNA-derived protein accumulates within the cell. 

One difficulty in framing this discussion is a lack of commonality in units for the expression systems. For example, the same substrate may not have been examined in all systems or activity may be expressed per mg total cell lysate protein, per mg cytosol-free cell membrane protein, per mg microsomal protein or per million cells. In this section, activity levels will be compared in the units originally reported. The following values, as determined in the human lymphoblast system, may be used to compare among the alternative methods of enzyme preparation cytosol-free membranes provide about a 2-fold enrichment in activity, microsomes provide 5-fold enrichment in activity and there are about 7 million cells per mg total protein. These ratios may differ somewhat for other mammalian cell systems but they are unlikely to be off by more than 2-fold. 

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