Baculovirus as versatile vectors for protein expression in insect and mammalian cells

Abstract

Today, many thousands of recombinant proteins, ranging from cytosolic enzymes to membrane-bound proteins, have been successfully produced in baculovirus-infected insect cells. Yet, in addition to its value in producing recombinant proteins in insect cells and larvae, this viral vector system continues to evolve in new and unexpected ways. This is exemplified by the development of engineered insect cell lines to mimic mammalian cell glycosylation of expressed proteins, baculovirus display strategies and the application of the virus as a mammalian-cell gene delivery vector. Novel vector design and cell engineering approaches will serve to further enhance the value of baculovirus technology.

Figure 1. Versatility of baculovirus expression vectors.

Baculovirus vectors can be used for a variety of applications. These include producing proteins in insect larvae, insect cells and mammalian cells. The insect and mammalian cells in the photomigrographs were treated with baculoviruses expressing GFP. Viruses can also be produced that display peptides or proteins on the surface of viral particles. The red circles on the schematic virus particle represent displayed gp64 fusion proteins.

Figure 2. Overview of processing pathways and major N-glycans produced by insect and mammalian cell systems.

The processing pathways in both systems yield a common intermediate. The major insect-cell end product (paucimannose) is produced by further trimming of this intermediate (left-hand branch), whereas the major mammalian-cell end products (including sialylated complex) are produced by elongation of this intermediate (right-hand branch).

Figure 3. Photomicrograph of mammalian cells transduced with a BacMam virus expressing GFP.

Virus as described in Condreay et al.. The cells were transduced with 100 plaque-forming units of virus per cell and photographed 24 hrs after virus addition. U-2 OS, human osteosarcoma, BHK, baby hamster kidney, HEK 293, human embryonic kidney and Saos-2, human osteosarcoma cells. Transduction frequency of these cell types is routinely greater than 90% as measured by the number of fluorescent green cells.

Figure 4. Production of BacMam viruses expressing G protein–coupled receptor (GPCR), ion channel (IC) and nuclear receptor (NR) target proteins and transduction of mammalian cells in microtiter plate-based high-throughput assay formats.

The system allows for a high level of flexibility in terms of target proteins, cell types and assay formats.