Recombinant protein production is the expression of proteins that have been produced by recombinant DNA techniques. This process enables these substances to be made in large quantities. Such mass production is done both for laboratory study and for industrial production.
This technique is often used to produce human growth hormone and insulin. Obtaining human growth hormone through recombinant protein production is a huge improvement over obtaining it from cadavers because the presence of proteins obtained from cadavers occasionally resulted in disease transmission. Making insulin in this way is also beneficial because it has enabled variants of insulin to be made that have different pharmacological actions in the body.
Proteins are chains of amino acids, encoded by DNA. The genes that code for these proteins are put into special vectors, or units of DNA. Vectors are chosen that will produce large amounts of the desired protein. This is known as overexpression.
Overexpression is done in special host cells. Sometimes the hosts are bacteria or yeast. In cases where the proteins are from mammals, the hosts are frequently insect or mammalian cell lines. A large number of kits are commercially available to facilitate both the cloning of the gene, and the subsequent recombinant protein production.
These kits have special vectors called expression vectors that have a special promoter to produce large amounts of protein. A promoter is the section of DNA that drives the production of the gene sequence that follows it. Frequently, these expression vectors can be turned off and are inducible. Especially with bacterial hosts, producing too much protein at once can be toxic, inhibiting the growth of the bacteria.
There are several different ways to induce expression. In both, the bacteria are grown to a certain density. Then either a compound is added for induction, or the temperature is shifted to one at which the promoter is active.
To facilitate the purification of the proteins from bacteria, the cloning is often done so that there is a tag on the protein that will bind to a matrix. This separates the protein from the cellular debris. For instance, a tag of histidine molecules on the protein will bind to a column of nickel. Once the protein is bound, the tag is cleaved off, leaving pure protein that can then be eluted from the column. It can take years to purify a protein using traditional methods.
An additional factor to consider is whether the protein requires modification after its initial production. This is often the case for mammalian proteins. Bacteria frequently do not properly modify such proteins, so overexpression of these more advanced proteins is often carried out in insect or mammalian cells. A number of biotechnology companies specialize in carrying out recombinant protein production.
