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Recombinant human protein is human protein that is produced from cloned DNA. This enables a scientist to express large quantities of it. Such overexpression has been of great utility for modern medicine, enabling the production of human protein-based drugs that have no other source. It has also led to great advances in the understanding of the function and biology of human proteins.
An example of a recombinant human protein that has no other source is the anti-anemia drug called erythropoietin. This hormone controls the production of red blood cells. It is used to treat anemia from various sources, including chronic kidney disease and cancer. Erythropoietin has also been used as a performance enhancement drug by athletes.
Other proteins can be isolated naturally, but it is much easier to obtain large quantities by protein expression from cloned DNA. An example is human growth hormone, which is currently obtained for therapeutic use by recombinant techniques. The traditional method of isolation from cadavers sometimes resulted in diseases being transmitted. Insulin is another drug that is utilized as a recombinant human protein. Most of the insulin used by patients is obtained in this manner.
Protein production from cloned genes is feasible, because the genes can be cloned into expression vectors. These are specialized units of DNA that are designed to produce large amounts of protein by the use of specialized promoters. These promoters direct the production of the cloned gene sequence. Custom kits are available for protein cloning and expression.
Specialized host cells are required for the production of a recombinant human protein. These can be bacterial or yeast cells. Some proteins require special modifications, such as the introduction of sugars, and are expressed in more advanced cell lines, like mammalian or insect cell lines.
For bacterial cells, the proteins will be inside the cells, requiring extraction and protein purification to separate them from the bacterial proteins. This is facilitated by special techniques that are part of the cloning process. For instance, specialized binding sites can be cloned that enable the protein to bind to a matrix and be easily eluted. This can save years of developing protein purification methods. Recombinant human proteins expressed in mammalian cell lines are frequently secreted into the media, facilitating their isolation and purification.
Having the genes for the proteins available as clones enables a scientist to make custom proteins, altering them to have the properties one desires. For instance, some recombinant insulin has been genetically altered so that it will have different effects on the body. The ability to alter these proteins is very useful in biological research.
Being able to express a recombinant human protein has revolutionized biomedical research. When a scientist has cloned a gene, he or she can compare it to a huge database of known gene sequences. If the gene has a sequence that is highly similar to a sequence of a gene of known function, he or she can predict the function of that gene. That knowledge suggests which experiments to perform with the product of the gene, which is frequently a protein. Sometimes, there is no homology to other gene sequences, and the scientist has no idea of the function of the gene.
Expressing the product of the gene allows a scientist to assay for the function of the gene using biochemical techniques. This can enable him or her to identify the function of the gene. Also, he or she can do experiments with the messenger RNA (mRNA) produced directly from the gene and determine under what conditions, and in which tissues, the gene is expressed. This knowledge helps to narrow down in finding the function of the gene and to find out if it codes for a protein.
If a scientist does know the function of a protein, overexpression can provide large quantities of the protein to study its biochemical properties. He or she can make targeted mutations and see what effects they have on the properties of the protein. Another reason to obtain large quantities of protein is to crystallize the protein and study its three-dimensional structure. Protein biochemistry can be difficult to perform in any system, but it was particularly difficult to do with human proteins before the advent of recombinant human proteins.
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