Protein Expression Systems

The first choice of an expression system for the production of recombinant proteins for many investigators is E. coli expression system. In other words, E. coli protein expression system is now the most wide-used and economical expression system. Many proteins require special modifications that are available only in eukaryotic cells. Disulfide bonds are not usually formed inside bacterial cells and are rarely formed properly even when bacterial hosts secrete eukaryotic proteins.

The E. coli expression system has many advantages compared with other expression systems such as easy growth conditions and rapid biomass accumulation. Expressing eukaryotic proteins in eukaryotic cells that contamination with bacterial components can be avoided. Despite purification, bacterial components that are toxic or promote immune reactions may be present in traces if bacteria are used for production. Furthermore, some eukaryotic proteins are unstable or inactive after being made by bacterial cells.

1. Chemical modifications that form novel amino acids in the polypeptide chain.
2. Formation of disulfide bonds between correct cysteine partners.
3. Glycosylation.
4. Addition of a variety of extra groups, such as fatty acid chains or acetyl groups.
5. Cleavage of precursor proteins may be needed for secretion, correct folding, or activation of proteins.

Sino Biological can provide you high-quality bacterial protein expression service. 

Some cloned animal genes may need to be expressed in cultured mammalian cells. Mammalian shuttle vectors contain an origin of replication and an antibiotic resistance gene for growth in bacteria. In other words, mammalian shuttle vectors have features for producing recombinant proteins in mammalian cell cultures. Because most antibiotics do not harm mammalian cells, a different method of selecting the mammalian shuttle vector must be used.

A major issue with protein expression in mammalian cells is finding a cell with high levels of the recombinant protein. This single chosen cell is then used to generate large cultures. This ensures that the recombinant protein is identical throughout the culture. Many techniques are available to isolate single cells with high levels of recombinant protein such as limiting dilution cloning, cell sorting, gel microdrop technology and automated cell selection.

Mammalian transient expression systems enable flexible and rapid production of proteins. They are ideal for generating large amounts of protein within 1 to 2 weeks. Sino Biological offers mammalian transient expression recombinant protein services in CHO and HEK 293 cells. Click the button to get your mammalian expression recombinant proteins below. 

Mammalian cells are relatively delicate and have complex nutritional requirements. In contrast, cultured insect cells are relatively robust and can be grown in simpler media than mammalian cells. Insect-based expression systems have the additional advantage of providing post-translational modifications that are similar to mammalian cells.

The baculovirus-mediated insect protein expression system is based on the ability of recombinant baculovirus to infect insect cells, and the foreign protein that is encoded by the baculovirus is expressed by the cellular machinery. Insect cells are easy to grow for making recombinant protein. Insect cells are infected with a virus genome that has the recombinant protein gene. Rather than making viral particles, the infected insect cells make recombinant protein.

Baculovirus-meditated expression systems possess a number of advantages:
1. High expression levels driven by the strong polyhedrin promoter.
2. Ability of the insect cells to perform a variety of post-translational modifications.
3. High capacity for multiple genes or large inserts.
4. Bio-safe and easy to handle.

Click the button below to inquire Sino Biological's high-efficiency expression of intracellular and extracellular proteins by baculovirus expression system.

In conclusion, which expression system is used is usually dictated by two things: the ultimate use of the product, and the nature of the individual protein to be expressed. Each expression system has its own unique strengths and weaknesses when it comes to
characteristics such as cost, speed, and ability to glycosylate or fold proteins.