Protein expression
Protein expression is a subcomponent of gene expression. It consists of the stages after DNA has been translated into amino acids chains, which are ultimately folded into protein. Protein expression is commonly used by proteomics researchers to denote the measurement of the presence and abundance of one or more proteins in a particular cell or tissue.Protein expression systems include bacterial, yeast, baculovirus/insect, and mammalian expression systems.
E. coli Expression System
Escherichia coli (E. coli) is one of the most widely used hosts for the production of heterologous proteins and its genetics are far better characterized than those of any other microorganism. Recent progress in the fundamental understanding of transcription, translation, and protein folding in E. coli, together with serendipitous discoveries and the availability of improved genetic tools are making this bacterium more valuable than ever for the expression of complex eukaryotic proteins.
Yeast Expression System
Yeast is a eukaryotic organism and has some advantages and disadvantages for protein expression as compared to E. coli. One of the major advantages is that yeast cultures can be grown to very high densities, which makes them especially useful for the production of isotope labeled protein for NMR. The two most used yeast strains are Saccharomyces cerevisiae and the methylotrophic yeast Pichia pastoris. Various yeast species have proven to be extremely useful for expression and analysis of eukaryotic proteins. These yeast strains have been genetically well characterized and are known to perform many posttranslational modifications. These single-celled eukaryotic organisms grow quickly in defined medium, are easier and less expensive to work with than insect or mammalian cells, and are easily adapted to fermentation. Yeast expression systems are ideally suited for large-scale production of recombinant eukaryotic proteins.
In some instances the most cost-effective expression of functional enzymes is the yeast expression system.
The major advantages of yeast expression system are:
High yield, High productivity ,Chemically defined media, Product processing similar to mammalian cells, Stable production strains,Durability,Lower protein production cost.
Insect Cell Expression System
Insect cells are a higher eukaryotic system than yeast and are able to carry out more complex post-translational modifications than the other two systems. They also have the best machinery for the folding of mammalian proteins and, therefore, give you the best chance of obtaining soluble protein when you want to express a protein of mammalian origin. The most commonly used vector system for recombinant protein expression in insect is baculovirus, although baculoviral also can be used for gene transfer and expression in mammalian cells
Mammalian Expression System
The production of proteins in mammalian cells is an important tool in numerous scientific and commercial areas. For example, the proteins expressed in and purified from mammalian cell system are routinely needed for life science research and development. In the field of biomedicine, proteins for human therapy, vaccination or diagnostic applications are typically produced in mammalian cells. Gene cloning, protein engineering, biochemical and biophysical characterization of proteins also require the use of gene expression in mammalian cells. Other applications in widespread use involve screening of libraries of chemical compounds in drug discovery, and the development of cell-based biosensors.
Insect Cell Expression System
Insect cells are a higher eukaryotic system than yeast and are able to carry out more complex post-translational modifications than the other two systems. They also have the best machinery for the folding of mammalian proteins and, therefore, give you the best chance of obtaining soluble protein when you want to express a protein of mammalian origin. The most commonly used vector system for recombinant protein expression in insect is baculovirus, although baculoviral also can be used for gene transfer and expression in mammalian cells
Mammalian Expression System
The production of proteins in mammalian cells is an important tool in numerous scientific and commercial areas. For example, the proteins expressed in and purified from mammalian cell system are routinely needed for life science research and development. In the field of biomedicine, proteins for human therapy, vaccination or diagnostic applications are typically produced in mammalian cells. Gene cloning, protein engineering, biochemical and biophysical characterization of proteins also require the use of gene expression in mammalian cells. Other applications in widespread use involve screening of libraries of chemical compounds in drug discovery, and the development of cell-based biosensors.