PROTEIN EXPRESSION SYSTEM EVALUATION AND SELECTION

Your protein is not expressing at optimal yield and activity? You tried to vary all kind of parameters without success? Maybe it is time to think about changing your protein expression system! Try our protein expression system evaluation and selection service and test up to 5 expression systems to offer a good start to your project!

What are the factors to consider when
choosing a protein expression system?

Choosing the most appropriate expression system is one of the most important factors to consider in recombinant protein production. A poor choice can essentially lead to poor expression yields or to inactive protein expression. ProteoGenix developed a protein expression system evaluation and selection service in order to help you make the right decision. A first approximation on the expression systems to consider can already be done before the beginning of the project. Here is a short list of criteria to consider:

• The characteristics of your protein: One of the main factor governing the choice of the right expression systems corresponds to the characteristics of your protein: mass of the protein, number of disulfide bonds, desired post-translational modifications…
• The type of protein you need to express: If the protein you need to express originates from a prokaryotic organism, a bacterial expression system will of course be favored. If your protein is from eukaryotic origin, many other eukaryotic expression systems can be considered depending on your requirements.

• Solubility of the protein expressed in E.coli: Bacterial expression systems allow for rapid, high yield and cheap protein expression. Thus, it is often generally the first expression system to test before considering eukaryotic systems. However, many eukaryotic proteins do not fold properly in E. coli and form insoluble aggregates known as inclusion bodies(which can be resolubilized). If this happens, eukaryotic expression systems should be considered because they possess more adapted protein folding machinery limiting the risk of insolubility..

• The need of post-translational modifications: In some cases, proteins need post-translational modifications to become active or to adopt their native structure. In this case, choosing the right expression system can be tricky as each eukaryotic cells perform different post-translational modifications.

What are the most common protein expression
systems?

Bacterial Expression Systems

E.coli and more generally bacterial expression systems are widely used because they are easy to culture, fast growing and resulting in high yield protein expression. These characteristics make from E.coli the most affordable expression system, especially for prokaryotic protein expression. In some cases, bacterial expression systems can also express eukaryotic proteins. However, the risk to obtain non-functional proteins should not be neglected as prokaryotic cells are not equipped to make proper folding and post-translational modifications. In those specific cases, eukaryotic expression systems are generally preferred.

Yeast Expression Systems

Yeast expression systems combine some benefits of bacterial expression systems with those of eukaryotic expression systems. These systems are particularly appreciated for their fast-growing and easy to manipulate genome and for their improved folding, disulfide bond formation and post-translational modification capacity (compared to bacterial expression systems such as E. coli). Also, as yeasts secrete very few endogeneous proteins, the purification step is facilitated.

Baculovirus/ Insect Cells Expression System

Baculovirus/insect cells expression system is able to carry out protein expression with modifications similar to mammalian cells. As they are considered as higher eukaryotic systems than yeast, they are able to perform complex post-translational modifications. Also, they can express most of the mammalian proteins in a soluble form thanks to their complete protein folding machinery.

Mammalian Expression System

Mammalian expression systems are able to reproduce the native structure and activity of mammalian proteins. As protein activity is related to the sequence, conformation and modifications, mammalian protein with optimal activity are generally expressed directly in mammalian cells.
Mammalian cell lines allow for transient expression or for stable cell line generation which could be a good option for long-term projects.

Our multi-system protein expression service can include from 2 to 5 different expression systems in order to provide you a solution that fully matches your requirements. Describe your project to our PhD account manager who will be glad to guide you in the right direction.