Cellular protein synthesis

Exploring recombinant protein expression using a baculovirus-insect cell system.

Proteins are essential for various cellular functions, making them a focal point of scientific inquiry across disciplines. Understanding the structure and function of proteins is crucial for unlocking the ‘mysteries of life’, driving research efforts across several scientific fields. However, obtaining proteins for study can be challenging due to their complexity.

Recombinant protein expression is a method that can help solve this problem since it produces proteins by cloning the gene of interest into an expression vector and introducing it into a host cell. The selection of the optimal host cell system is critical for successful protein expression. One such system is the Baculovirus-insect Cell System (BEVS), which utilises baculoviruses to deliver target genes into insect cells for protein production.

The BEVs process

In the BEVS process, a gene encoding the protein-of-interest is inserted into a primary vector and then cloned into a secondary vector known as Bacmid. This Bacmid is transferred into a bacterial strain for preliminary virus production, resulting in the generation of baculovirus (Figure 1). The baculovirus is then amplified in insect cells and used to infect insect cell lines for protein expression, offering a versatile platform for producing various proteins.

Application of BEVS

Insect cells are often used to produce large molecular weight (MW) proteins (MW> 150 kDa) because of their superior folding and post-translational modification capabilities. One major downside of this endeavour, however, is the structural complexities of such proteins, which often results in relatively low yields (Fig. 2, left). One alternative approach is to express a domain-of-interest rather than the entire protein; however, in the case presented here, the direct expression of two enzyme domains of human fatty acid synthase (FASN) was not feasible because of low protein yield and heavy degradation (Fig. 2, middle). By extrapolating and fusing the sequences encoding the methyltransferase and ketoreductase domain with a linker, Sino Biological successfully obtained a high-yield construct (Fig. 2, right). The Elute 1 and 2 of this construct were pooled and further purified to yield a final fusion protein with >90% purity. It should be noted that some proteins require certain oligomeric formations to be functional. For example, the hemagglutinin proteins of influenza virus and the spike protein of SARS-CoV-2 exhibit a trimeric format, whereas the human prolyl endopeptidase, FAP, is an intrinsic dimer.

Conclusion

Recombinant proteins are fundamental to the study and development of biologics. Insect cells are a superior choice as an expression host because they enable correct protein folding and posttranslational modification, and are suitable for high-density cell culture. In addition, they can produce both secreted and intracellular proteins of various species.

For more information visit Sino Biological.

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