Proteins

Recombinant proteins are made through genetic engineering, also called gene splicing or recombinant DNA technology. By putting human, animal or plant genes into the genetic material of host cell expression systems these microorganisms can be used as factories or producers to make proteins for medical, academic and research uses.

For DNA to be manipulated it must be placed within a “transport vehicle” in which proteins may be produced from the genetic code of the DNA. Some of the most common host cells used for recombinant protein synthesis include; mammalian cells, bacteria, yeast cells, or insect cells.

The 5 main stages of recombinant protein generation are outlines below:

Figure: Schematic representation of the synthesis of Recombinant Proteins

The synthesis of recombinant proteins begins with the identification of the genes of interest; the gene(s) that will encode the protein of interest. To isolate these genes from the native genome, DNA is treated with restriction enzymes known as endonucleases. These enzymes “cut” the gene of interest out of the genome preparing it for the cloning steps.

Cloning is the process by which the gene(s) of interest are then inserted into an expression vector and expressed. Before this occurs however, the fragment of interest must be amplified. This step is necessary as the genetic material of interest must be in a large enough quantity for the subsequent sequencing steps. This is often carried out by polymerase chain reaction (PCR). PCR is the most common in vitro method of cloning. However, cloning may also be carried out in an in vivo setting. The most common in vivo method of cloning is done within the bacterium E.Coli.

Following amplification, the vectors must then be introduced into their host cell. Vectors may already be in their host cells if amplification is carried out in an in vivo setting. However, if replication is carried out in vitro, the host cells are prepared for the uptake of genetic material, either via mechanical (e.g. electroporation, microinjection) or chemical (e.g. calcium phosphate, heat shock) transfection methods.

Significant amounts of recombinant protein are produced by the host only when expression genes are added. The protein’s expression depends on the genes which surround the DNA of interest. This collection of genes act as signals which provide instructions for the transcription and translation of the DNA of interest by the cell. These signals include the promoter, ribosome binding site, and terminator.

The piece of DNA that is inserted into the vector often has other important non-coding regions which have specific functions. These regions allows scientists to distinguish which cells have incorporated the recombinant genetic molecules, as well as allow the gene to be expressed. For example, the antibiotic-resistance gene allows the host cell to survive in its residing medium that is antibiotic-rich. Those host cells which have not taken up the vector as a result do not express the gene which is necessary for resistance to antibiotics, and thus the organism dies.

The vector often contains a tag in addition to the specific DNA sequence; this facilitates the purification of the recombinant protein. This is often added at the N-terminal end of the amino acid sequence. One of the most common tags used in recombinant DNA technology is the hexahistidine tag (His-Tag). This is a sequence of 6 histidine residues that act as a metal binding site for recombinant protein purification and expression. The His-Tag contains a cleavage site for a specific protease. His-Tag recombinant proteins are purified by Metal Chelate Affinity Chromatography such as nickel ion columns that are used as the heavy metal ion and the His-Tag protein is eluted from the metal-chelate column with Histidine or imidazole. Then the purified His-Tag protein is treated with the specific protease to cleave off the His-Tag or not if the tag doesn’t affect the active site of the protein.

The resultant product is the fully formed recombinant protein. Amplification not only occurs during the PCR step but also at this stage, as host cells have the potential to produce thousands of proteins once the vector is uptaken.

Recombinant proteins have a wide range of applications. Some of their main uses include:

Recombinant proteins may be used to treat diseases. They may be given to patients who are deficient in a particular protein, or those that have an abnormal version of a protein e.g recombinant insulin in diabetes, recombinant human growth hormone (HGH). Alternatively, proteins may be recombinantly synthesized to treat diseases such as cancer or infectious diseases by targeting causative agents of disease (e.g. Immune checkpoint inhibitors). Recombinant proteins also have the ability to fight disease by acting as vaccines e.g. SARS-CoV-2 recombinant proteins from Assay Genie (*intended for research use only). Furthermore, recombinant proteins may be used in the diagnosis of disease; the majority of proteins used as a part of biomedical diagnostic tools are recombinant.

Recombinant DNA technology has progressed proteomics research significantly over the past number of years. As explained above, its discovery has made scientific investigations much easier and quicker to be carried out. Recombinant proteins help to elucidate the mechanisms underpinning the function of naturally occurring proteins in a controlled environment. They also have several uses in key laboratory assays such as Western Blot, ELISA, and immunohistochemistry where they can act as standards or controls.

An example of the use of recombinant proteins in research is the current global efforts to discover a potential therapy for COVID-19. Recombinant proteins of components of the SARS-CoV-2 coronavirus have been created. By investigating the effects of targeting such proteins it may be possible to develop a novel therapy to fight the COVID-19 infection. Such recombinant proteins may also be used to synthesize a vaccine with the potential to kill SARS-CoV-2 viral molecules. Check out our SARS-CoV-2 recombinant proteins designed for COVID-19 research here.

Other applications of recombinant proteins include their use in the agricultural and food industry. Recently, recombinant DNA technology has been utilized to create some of the biggest breakthroughs in these industries. The widely known concept of genetically modified foods utilizes recombinant DNA technology to reduce crop failure and lengthen shelf-lives. An example of this is Bt corn; a toxin-producing gene (known as Bt (Bacillus thuringiensis)) is inserted into the genome of the corn plant. The resultant genetically modified plant is resistant to insects which causes disease in such plants. Recombinant proteins have also used in the agricultural industry in animal feed production to enhance its nutritional value (addition of recombinant enzymes), thus improving animal health.

Note: Assay Genie recombinant proteins are strictly for research-use only. Therefore, their use in humans, or in any biotechnological application other than research, is not permitted. They may however be used in an in vivo setting using animal models to gain insight into their therapeutic benefit.

Recombinant proteins function according to the protein they have been created to resemble. Proteins may have several different functions. This depends on the subgroup which the protein belongs to. Some subgroups of proteins include: