Protein expression systems are biological processes employed to synthesize certain proteins on a large scale for investigation, application, or treatment. These systems enable scientists to produce proteins by inserting the gene that codes for the wanted protein into a host cell which in turn uses its own components to give rise to the protein.
There are various types of protein expression systems available, and each of them has its specific advantages in terms of type of protein, yield, and application.
Bacterial
E.coli bacterial systems are used most frequently because of their easy manipulation and fast growth coupled with low cost. In this system, bacteria are genetically engineered by inserting the gene for the target protein into a plasmid which is then placed in the bacteria. That is, once the bacterial cells take in the plasmid, the cells themselves synthesize the protein in an identical manner.
Key Benefits:
- Facilitating bacterial proteins allows bacterial cells to form as well as synthesize considerable amounts of protein within a short period.
- Essentially few pieces of equipment and low-cost growth media are used.
- Easy-to-follow procedures and no special equipment are required.
Yeast Expression
S cerevisiae, P pastoris, etc are yeast organisms, and they get involved in post-translation modifications, which are often the difference between eukaryotes. Yeast systems are intermediate between bacterial and mammalian systems and perform some of the post-translational modifications, but the cost of production is relatively high and yield is good.
Key Benefits:
- Yeasts also carry the ability to glycosylate proteins and process them as mammalian cells do.
- Such yeast systems for that matter are used frequently and they yield higher than the mammalian cells.
- Compared to mammalian cells, yeast cells are less oncogenic and also easier to manipulate genetically.
Insect Expression
Insect cells derived from baculovirus hosts such as the Spodoptera frugiperda (Sf9) or Trichoplusia ni (High Five) cell lines are used in the baculovirus expression vector system (BEVS) to synthesize recombinant protein. In this system, baculovirus infects insect cells in which the required protein is synthesized.
Key Benefits:
- Insect cells can also perform many modifications but with less accuracy than mammalian cells.
- Insect cells offer high yield, correct protein folding, and biological activity of produced proteins.
Mammalian Expression
CHO cells and HEK cells are used to produce proteins that require specialized post-translational processes such as glycosylation, phosphorylation, or refolding. This makes mammalian systems suitable for generating therapeutic proteins including antibodies, hormones, and enzymes.
Key Benefits:
- Mammalian cells are capable of glycosylation and other modifications of proteins that are required for therapeutic proteins.
- Mammalian cell-expressed proteins are postulated to have higher probabilities of achieving their native folded state and also being biologically active.
- Protein, especially for medical use can be produced appropriately using this approach.
Cell-Free Expression
Cell-free systems do not require living cells at all as a substrate for protein expression. However, these systems employ test tube production of protein where proteins are synthesized by a cocktail of cell parts such as ribosomes, enzymes, and amino acids. Because they do not rely on live cells, cell-free systems provide a relatively quick option for protein synthesis, which is beneficial for proteins that might be hazardous to cells.
Key Benefits:
- It is possible to generate proteins in a matter of hours.
- Some proteins that are toxic in a live sample or extremely hard to express can be produced easily without limitations such as living cells.
- It must also be noted that reaction conditions can be fine-tuned for higher expression of specific proteins.
Conclusion
Recombinant protein expression systems are critical components for generating protein complexes for both research and commercial usage. These both have different effective functions that make them applicable in different circumstances and types of proteins. Bacterial and yeast expression systems are economical and give high yield for less complicated proteins while mammalian and insect expression systems are compact for synthesizing more complicated proteins requiring further modifications. Cell-free systems are the perfect match for certain purposes because of their flexibility and the short time it would take to get a result. Choosing an effective system remains as the key to advancing the synthesis of functional and properly folded proteins.
