Viral recombinant protein production factories

Viral recombinant protein production factories

Recombinant proteins are of vital importance in biotechnology as they are used to produce a variety of useful molecules for commercial and research use such as antibodies, enzymes, vaccines and biopharmaceuticals. Recombinant proteins are proteins produced from recombinant DNA technology and the majority produced use bacterial, fungal, or virus expression systems. These systems are of major importance as they may be altered to allow tailoring of the proteins produced to match the specific requirements of their uses such as secretion and post transcriptional modifications. Study of virus protein expression systems are of specific usefulness as unlike many bacterial expression systems, they allow for eukaryotic post transcriptional modification.

One type of virus recombinant protein expression is the baculovirus that is used with insect cell lines mainly of the Lepidoptera order. Baculovirus are rod shaped viruses with double stranded DNA that have very limited hosts such as moth and butterfly larva. This expression system uses the baculovirus, the larvae cell line and a transfer plasmid containing the gene for the protein wanted linked to a viral promoter. The virus and the plasmid are transfected into the cell line where they are replicated by the virus as part of its natural infection cycle; the protein is produced in the late phases of the infection. The advantages of this expression system is the ease in which the plasmid used can be altered to incorporate multiple genes, increase the expression or add signal sequences to cause the recombinant protein to be secreted for easy purification. The disadvantage of this system is that the post transcription modifications done by the host insect cells are not the same as used in mammals. This can cause allergic reactions in people and this limits the use of proteins produced in this way for medical purposes.

Another viral expression system of importance is the use of simian immunodeficiency virus (SIV) along with African green monkey cell cultures and a recombinant plasmid to produce required recombinant proteins. The virus and the plasmid transfect the cells in culture, the plasmid and the virus are then rapidly replicated within the cell because the plasmid contains the viral origin of replication. This plasmid can then produce vast quantities of recombinant proteins as it has many copies of its DNA from which to transcribe. The advantages of this expression system are that the African green monkey cells use the same post translational modifications, mainly glycosylation, as human cells. The main disadvantages of this expression system are that it is very expensive and is unable to be used for continuous protein production so must be used for batch as the uncontrolled replication of the plasmid will cause cell death.

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