Recombinant protein synthesis requires introducing the desired gene into cells using a DNA vector. Using the host cell’s machinery, the gene is subsequently translated into a protein using the host cell’s machinery. These expressed proteins were obtained after a series of purification procedures and cell lysing. Protein manufacturers and researchers use both prokaryotic and eukaryotic expression systems. Each expression system is chosen depending on its advantages, the type of protein required, protein yield, and qualitative and economic aspects.
The following article will examine some pros and cons of protein production expression systems.
Bacterial Expression system
Most researchers and protein expression service providers prefer using bacterial expression systems. This is due to the following advantages:
- They give a high yield of recombinant protein.
- They are simple, and their genetics are not complex
- Bacterial expression systems have a low culturing cost
- It has a well-formed labeling protocol hence ensuring stable studies
- Bacterial expression systems are easy to scale up through fermentation
However, there are several disadvantages associated with bacterial expression systems. They include:
- It’s hard to express specific mammalian proteins using the bacterial expression system
- It leads to the accumulation of proteins as inclusion bodies
- The yielded protein is contaminated with protease, leading to low-quality production.
- Bacterial expression systems are accumulated with endotoxins.
Yeast Expression System
The yeast expression system is a eukaryotic organism used in protein production. Most industries and biopharmaceuticals have used the yeast expression system for large-scale protein production. Through a well-defined medium, yeast can be grown to high cell mass densities. Advantages of using a yeast expression system include;
- Since it’s a well-established industrial fermentation system, It supports the production of high-quality recombinant protein.
- It has a controllable process. This is because the medium responsible for feeding yeast is well defined, and the formulation is simple and inexpensive. Further, the process used in protein expression through the yeast system is regulated to minimize any toxic effect in the yeast by foreign protein.
- Yeast expression systems use less expression time.
- This system produces mammalian-like protein since it’s a eukaryotic system.
- As a eukaryotic system, the Yeast Expression System produces mammalian-like proteins.
- It supports post-translational protein modification and processing.
Some of the drawbacks associated with the yeast expression system include; the yeast system lacks a strict and strongly regulated promoter, it has low-efficiency secretion, it’s hard to express proteins with large molecular mass, and lastly, they are not suitable for high-density cultivation.
Insect cell expression system
When using an insect cell expression system, you can’t ignore the baculovirus-based method. It mainly expressed mammalian proteins, especially those requiring posttranslational modification. The desired gene is inserted into baculovirus vectors in the yeast system and transferred into cultivated insect cells.
Some of the advantages associated with the yeast system include; it enables the production of high-level proteins with simple posttranslational modifications and glycosylation, it is easy to scale up, the purification process is simple, and it is safe to work with baculoviruses compared to mammalian viruses. It has a simplified cell growth that can easily be applied in high-density suspension culture during large-scale protein production.
Yeast systems have drawbacks, such as the cloning process of the desired gene in baculovirus is long and time-consuming, it requires costly media, and the glycosylation may lead to improper maintenance of epitopes on proteins.
Mammalian Expression System
The mammalian expression system is mainly used in producing mammalian proteins with the most native activity and structure. The mammalian system is commonly preferred for studying the function of a specific protein, especially in a given physiological environment. This is because it allows for the highest level of posttranslational functional activity and protein processing. Most researchers use this system to produce therapeutic proteins and antibodies.
The advantages of using mammalian expression systems include; that they are the best for the expression of therapeutic protein and vaccines, they can allow the expression of protein through transient and stable cell cultures, and they also offer needed posttranslational modification and efficient folding of the protein.
Disadvantages of the mammalian expression system include; it is costly due to; slow cell growth, use of expensive media, and culture conditions such as the constant supply of carbon (IV) oxide and expensive transfection agents. Further, high yields of protein can only be obtained through suspension cultures.
Cell-free expression system
A cell-free gene expression system was developed as an alternative technique to living cells for specific applications in protein production. This system has some tremendous advantages that have made it a preferred technique for protein expression in synthetic biology and bioengineering. Some of these advantages include allowing protein expression in a cell-free environment through cell extract, amino acids, DNA templates, and co-factors. The process is simple; the expression and purification of protein can be done within a short time and hence time efficient.
Nevertheless, the cell-free expression system has some drawbacks, such as exogenous proteases from the cell extracts may degrade protein quality. Further, the extracts are very expensive, making the whole process very costly.
Understanding the pros and cons of these protein expression systems help you make the right choice on the type of system to use. However, the type and purpose of the protein required may dictate the type of expression system used.