The Baculovirus Expression Vector System (BEVS)

The Baculovirus Expression Vector System (BEVS) is used to produce recombinant proteins. This is very useful in regards to virology studies and biotechnology applications.

Baculovirus on ice ready to be harvested. Image Credit: flukestockr / Shutterstock

A baculovirus is an enveloped double-stranded DNA virus that belongs to the Baculoviridae family, which affects approximately 600 different insect species. Baculoviruses are one of the most studied insect viruses, with applications in both virology and biotechnology.  

The most widely used baculovirus species for basic virology and biotechnology is Autographa californica multiple nucleopolyhedrovirus (AcMNPV).

What is the Baculovirus Expression Vector System (BEVS)?

The insect cell-based BEVS has been extensively used to produce many diverse types of recombinant proteins for research, medical, agricultural, and veterinary purposes.

Recombinant gene production

Recombinant AcMNPV-infected insect cells produce a huge amount of recombinant proteins.  The baculovirus polyhedrin or p10 is normally highly expressed during the late stages of infection and is not essential for the pathogenesis and replication within a host insect cell.

The baculovirus polyhedrin or p10 can be replaced with a gene of interest, which allows for the promoters to expresses the gene in abundance allowing for a very high concentration of the gene of interest to be made.  

Vectors for gene delivery

AcMNPV is a virus that can only infect insects. Past studies discovered that mammalian cells were able to internalize baculovirus. Other studies subsequently discovered that recombinant AcMNPV can infect mammalian cells. Recombinant baculovirus can be combined with several different proteins in order to target different cell types.

To target hepatocytes, the Rous sarcoma virus (RSV) promoter is used to mediate the expression of the lacZ gene. Baculovirus can mediate gene expression in the immortal HeLa cell line or the fibroblast-like COS-7 cells, by using chimeric CAG promoters consisting of CMV immediate-early enhancer, chicken β-actin promoter, and rabbit β-globin polyadenylation signal.

These discoveries have allowed for a greater number of cell lines and cell types to be transduced by baculovirus, as well as the wider use of baculovirus for in vivo gene delivery systems.

Improving the baculovirus expression vector system

Thousands of recombinant proteins have been produced in baculovirus-infected insect cells since the conception of the BEVS in the 1980s. The BEVS contains several bottlenecks that hinder the efficiency and use of it.

One bottleneck of this system is that the expression yields from insect cells are significantly lower than those achieved from most mammalian cells. This is not a huge downside as the system compensates for this in terms of saving time to acquire results and produces lower costs.

Another problem that arises with the BEVS is that marked proteolysis of recombinant proteins during the baculovirus-based production regularly occurs. This is due to the structural changes within a host following a viral infection (referred to as the cytopathogenic effect).

Researchers have been working on increasing BEVS productivity using special transfer vectors, which encode resident fusion proteins and improve the protein expression of recombinant baculoviruses. The deletion of non-essential virus genes, such as p26, p10, and p74, also increases productivity.

Perspectives

Baculoviruses are very diverse and have applications in many areas of scientific research and technology. Baculovirus can be used as vectors for recombinant protein production or vehicles for gene delivery. The versatile characteristics of baculoviruses make them one of the most studies insect viruses.

Future studies into baculoviruses and the BEVS will provide more efficient methods that can overcome the complications and bottlenecks that were previously discussed. More research will also provide more proteins that can be made using the BEVS and more ways in which the BEVS can be used.

Further Reading

• All Plasmid Content
• What are Plasmids?
• All Virology Content
• Virology – What is Virology?
• Viral Diseases

Written by

Samuel Mckenzie

Sam graduated from the University of Manchester with a B.Sc. (Hons) in Biomedical Sciences. He has experience in a wide range of life science topics, including; Biochemistry, Molecular Biology, Anatomy and Physiology, Developmental Biology, Cell Biology, Immunology, Neurology  and  Genetics.