Question

You are given three therapeutic proteins; insulin, erythropoietin and G-CSF. In what production systems would you produce these proteins, and why? Which would form inclusion bodies and why?

Answer 1

Proteins that are engineered in the laboratory which are effective against several diseases and disorders are called therapeutic proteins. They are widely used in pharmaceutical industries.

The process by which a specific protein is engineered or generated in laboratory is called protein production. Production of protein is carried out with the help of protein production or expression systems. The different production systems include bacteria, yeast, insects, or mammalian systems.

Insulin

Insulin is a therapeutic protein whose structure is similar to that of naturally occurring human insulin. It is produced using the expression system derived from Escherichia coli or Saccharomyces cerviceae. Using this, recombinant DNA is synthesized with the help of recombinant DNA technology. S. cerevisiae is the most preferred and predominant yeast for large scale commercial production of insulin. E. coli is used in insulin production because of its high growth rate, easy handling, requirement of simple media, and cost effectiveness. Hence, large quantity of insulin can be obtained using these expression systems and also reduces the risk of host viruses, toxins, and prions.

Erythropoietin

Pichia pastoris (a yeast) expression system is used for the production of Erythropoietin. P. pastoris can be cultured and maintained easily and share some important biological characteristics with eukaryotic cells. P. pastoris can grow with simple alcohol methanol as its only energy source and are able to produce high cell densities thus producing large quantities of proteins with minimal lab technologies.

G-CSF (Granulocyte colony stimulating factor)

It stimulates the bone marrow to produce stem cells and granulocytes. G-CSF is synthesized in an E.coli expression system. E.coli has a fast growth rate, good protein production rate, and undemanding growth conditions. E.coli can also be stored frozen and need not be used immediately.

Nuclear or cytoplasmic aggregates of proteins are called inclusion bodies. They are formed during viral multiplication in bacteria and mainly consist of viral capsid proteins.

Inclusion bodies are more formed in E. coli. Proteins formed in the cytoplasm of the bacterial cell becomes incorrectly folded and form insoluble aggregates. This is because bacteria are not equipped with enzymatic machinery to undergo the required post-translational modifications. Thus, such proteins in the cytoplasm form inclusion bodies which are difficult to recover.

Hence, E. coli expression systems tend to produce inclusion bodies.