Baculovirus Expression System: A Powerful Tool For Protein Production

Introduction

How Does it Work?
Baculoviruses are large,double-stranded DNA viruses that infect specific insects like moth and butterfly species. The most commonly used baculovirus is Autographa californica multiple nucleopolyhedrovirus (AcMNPV). In the baculovirus expression system, a gene of interest is inserted into the genome of AcMNPV using a transfer vector. This recombinant baculovirus is then used to infect insect cell lines, most commonly Sf9 or Sf21 cells derived from Spodoptera frugiperda. Inside the insect cells, the recombinant baculovirus will hijack the host cell’s machinery to produce large amounts of the protein encoded by the inserted gene. Cell lysis occurs after 3-5 days of infection, releasing high levels of the recombinant protein into the culture medium.

Advantages of the Baculovirus Expression System

Post-translational modifications: Insect cells are capable of performing many eukaryotic post-translational modifications such as glycosylation, acetylation, phosphorylation etc. This allows production of properly folded and functionally active eukaryotic proteins.

High yields: Baculovirus systems are capable of producing gram quantities of recombinant proteins per litre of insect cell culture. Yields obtained are usually 100-1000 times higher than prokaryotic systems.

Insect cells grow to very high densities: suspended Sf9 and Sf21 cultures can reach densities of 1-3x106 cells/ml. This further enhances the protein yields.
 Low cost: The use of serum-free medium and cultivation in bioreactors has significantly reduced the production costs. It is more economical than mammalian cell cultures.

Easy scale-up: Baculovirus-infected insect cell cultures can be easily scaled up in bioreactors from research lab to industrial scale. This allows production of kilograms of protein from a single batch.

Applications of Baculovirus Expression System
Proteins expressed using the baculovirus system find wide applications in biotechnology, medicine and research. Some major applications are:

Production of viral vaccines: Viral capsid proteins, subunit vaccines, viral receptor proteins have been produced for vaccine manufacturing against Hepatitis B, Human Papilloma virus etc.

Pharmaceutical proteins: Recombinant clotting factors, monoclonal antibodies, cytokines and growth factors are produced in high yields for therapeutic purposes.

Enzyme production: Proteases, Baculovirus Expression System etc. are needed for various industrial and research applications.

Structural biology: High yields of membrane proteins, toxic proteins needed for crystallography studies are facilitated by baculovirus.
 Nanoparticles: Virus-like particles, lipoprotein nanoparticles self-assembling from recombinant proteins are being explored for drug/vaccine delivery.

Molecular biology tools: Green fluorescent protein (GFP), β-galactosidase (β-gal) used widely as reporter proteins are regularly expressed using baculovirus.