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Researchers in Germany have demonstrated that a simple method for protein purification from plant leaves is opening the door for the production of drugs known as biopharmaceuticals at lower costs and larger quantities than current methods by Daniela Kenzelmann.
Currently, certain proteins can be purified from a plant through a method called inverse transition cycling. In order to extract a desired protein from a plant, however, it is necessary to use a water-based solution. The only problem is once in water, proteins do not separate readily.

Now, Dr. Scheller's group at the Biochemical Institute in Kiel in collaboration with the Leibnitz-Institut fuer Pflanzengenetik und Kulturpflanzenforschung (IPK) in Gatersleben took advantage of a special tag named ELP-tag can help over come this problem.

When the ELP-tag is added to the protein to be purified, researchers can raise the temperature to 40 degrees Celsius, at which point the protein will separate from the water, this process is called precipitation. The precipitated protein of interest can subsequently be collected by a simple centrifugation

However, when a protein is heated, it often loses its shape, which can also mean it loses its ability to carry out its function. That is why it is crucial that the protein to be isolated re-adopts its original form after the heating step. Otherwise its biological activity will be lost, and the drug the drug rendered useless.

Although only the ELP-tag facilitates the separation of the desired proteins, the heat could harm the rest of the protein which constitutes the therapeutically active agent. The inverse transition cycling method has already been used to produce spider silk proteins, which are known to be particularly resistant to heat.

In this work, Dr. Scheller's group provides an example that therapeutical proteins can be purified by this method and even more importantly, that the purified protein still retains its medical benefit afterwards.

Application with sgp130

Research has identified interleukin-6 (IL-6) as a crucial signaling molecule implied in the pathogenesis of Crohn's disease, rheumatoid arthritis and colon cancer. The soluble glycoprotein 130 (sgp130) is a valuable therapeutic target, because it can bind IL-6, thereby preventing the development of disease.

For their work, Dr. Schellers group used a modified version of sgp130 which is able to bind IL-6 and fused it to the ELP-tag. This fusion protein was produced in tobacco leaves and harvested by inverse transition cycling in large amounts.

In anticipation of a future therapeutic use, the researchers tested the IL-6 binding capacity of the purified protein and its ability to block signals elicited by IL-6 in the target cells. Dr. Scheller's work also showed that the sgp130 was still active.

Commenting on the recent publication, Dr. Scheller told Checkbiotech that, "Production of pharmaceuticals from transgenic plants at low cost will improve the public acceptance of this technology."

However, this purified protein still contains the ELP-tag, which is large and could disturb the function of the therapeutic protein or provoke adverse interactions. Thus, future studies from Dr. Scheller's group will be aimed at engineering of a sgp130-ELP protein where the ELP-tag can be cleaved off after purification.

Daniela Kenzelmann is a Science Journalist for Checkbiotech and is writing her PhD at the Friedrich Miescher Institute in Basel, Switzerland.



[www.ncbi.nlm.nih.gov]