High quality eukaryotic proteins - optimized eukaryotic expression system
Currently, prokaryotic and eukaryotic expression system are the most common used protein expression systems. And eukaryotic expression system contains yeast, mammalian and insect cell expression system, .
The prokaryotic expression system is famous for its economic and efficient, but it is lack of post-translational modification. Hence, to some extent, proteins expressed by this system regularly do not possess bio-activity. The insect cell expression system involves the use of baculovirus, so it also has its own limits. Yeast expressed proteins have high level of expression, and they are easy to purify, but the proteins are also prone to degrade and the expression processes are hard to control. The mammalian cell system possesses natural post-translational modification, so, recombinant protein expressed by this way will be similar to natural protein, hence it regularly has bio-activity. But this system also had another coin-side: high cost and low expression level.
So when we built protein expression platform, besides prokaryotic and yeast expression systerm, in order to obtain protein with bio-activity, the mammalian cell system was also established. In this mammalian cell system, we have optimized various conditions to increase the expression level. The optimization and their effects are listed in table 1.
Table1. The optimization and their effects of mammalian cell system
| The optimization | The effect |
| Independent-constructed expression plasmid pCCC3 | Strong promoter and enhancer, increase the efficiency of transcription |
| 293F cell line | Increase the expression efficiency, human-derived cell lines could provide the same post-translational modifications while production of human proteins |
| Full-length sequence without signal peptide | Use full-length sequence, keep the bio-activity of protein |
| Affinity chromatography | Protein with high purity, eg: 98% |
Take human fibroblast growth factor (RPB882Hu61) for example, the yield of this protein derived from mammalian cells is about 110mg / L, and the purity is about 98% after purification (Figure 1).
Figure1. SDS-PAGE analysis of human fibroblast growth factor
（Lane1，2：Purified human fibroblast growth factor protein，Lane3：MW marker）
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