Insect cell protein expression

Baculovirus expression systems are eukaryotic expression systems. This confers to these systems all the advantages conferred by their eukaryotic nature such as:

• Proper protein folding: insect cells integrate the whole protein folding machinery characteristic of eukaryotic expression systems. Baculovirus is the most commonly used expression system for structural analysis (e.g. determination of 3D protein structure).

• Post-translational modifications: baculovirus expression systems are able to make post-translational modifications such as glycosylations and phosphorylations. These modifications confer improved solubility properties to the protein expressed compared to E.coli protein production and are very close to those found in mammalian cells.

• Ability to express large protein complexes of mammalian proteins.

They even include unique advantages compared to other eukaryotic systems such as:

• High level of protein expression (even if higher protein yields could be achieved using E. coli or yeast protein expression).

• Lower cost compared to mammalian protein expression.

To conclude, insect cells expression represents the best option for researchers and companies willing to produce their protein in a eukaryotic expression system (with glycosylation profiles close to those obtained in mammalian cells) at affordable price.

There are many factors influencing the yield of baculovirus protein expression. One of the most important is the multiplicity of infection (MOI). Multiplicity of infection refers to the number of virus to add to cells.

There are mainly two processes used for baculovirus protein expression:

• Low MOI process: this process refers to a two-steps baculovirus infection process. In the first phase, cells are inoculated with a MOI<1 resulting in only a partial infection of the cell culture. This means that uninfected cells continue to proliferate and that infected cells produce the recombinant protein and new virus particles. In this case, a second infection is necessary resulting in a high density infected cell culture. This method leads to longer processes but usually increases the yield of protein expression as more cells are available to produce the recombinant protein.

• High MOI process: the high MOI baculovirus infection corresponds to a one-step process where an excess amount of virus (MOI>1) is added to the cell culture.

The yield of insect cell protein expression can also be enhanced by optimizing the incubation time. The goal of this step is to determine at which incubation time the cell culture should be harvested. Basically, cell culture should be harvested before protein degradation starts.

As each project represents a unique challenge, ProteoGenix tests several cell lines, multiplicity of infections, incubation times and culture media (under request). Contact our PhD account manager to get your custom offer.

The baculovirus expression system is based on the infection of insect cells with baculovirus. Baculovirus are insect pathogens controlling the insect population in nature. They present a biphasic replication cycle driven by two forms of the virus:

• Budded virus: the form necessary for the infection of insect cell culture.

• Occlusion derived virus composed of a large amount of P10 and polyhedrin.

This latest form of the virus is not necessary for infection of insect cell cultures. Thus, the polh and p10 promoters can be exploited for recombinant protein expression. This is the basis of the baculovirus expression system.