22 Dezember 2003

Finding Lets Plants Produce Human Proteins

tobaccoNot for smoking: Genetically engineered tobacco could be a cheap and effective producer of therapeutic human proteins

A new discovery in plants could lead to their use for cheaply producing therapeutic proteins for humans.

Researcher Lokesh Joshi from Arizona State University in Tempe says that the discovery has both basic and applied applications. “It is a pathway, a set of chemical reactions, that had never been reported before in plants,” says Joshi. “The discovery will facilitate the use of plants to produce medically important proteins, in their correct form, for human use.”

Power plants
Plants have traditionally been the source of many drugs, including aspirin from willow bark and cardiac glycoside from digitalis. Their potential has been expanded by genetic engineering, which can create plants that produce human therapeutic proteins and vaccines. But a common problem with plant-produced proteins is that they are often seen as foreign substances by the human body and therefore rejected by the body’s immune system.

Sugar added
Researchers have found that this rejection is triggered by the proteins lacking an adequate amount of sugars called sialic acids. When these are present, the body doesn’t try to get rid of the proteins. Without the sugar groups, however, the immune system rapidly clears them away. “In humans, sialic acids protect the protein,” says Joshi. “They tell our body that this is a self-made protein. If it is not there on a glycoprotein, then our body says it is not a self-made protein and it needs to be removed.”

Chemical pathway
Joshi and colleagues discovered a pathway—a set of chemical reactions—common in humans and plants that attaches the sugar groups to proteins.

“What we discovered is that there is a very complex set of reactions that exist in plants and no one knows how it got there or what it is doing there, but it is similar to human beings,” says Joshi. Knowing that the pathway exists, he explains, researchers can work on making plants produce glycoproteins for humans.

Not sweet enough
So far, Joshi and his team have worked on three human proteins, an immune activator, a type of collagen and a heat shock protein , in the tobacco ,Arabidopsis and alfalfa plants. “We are seeing about two to three percent of sialic acids on proteins made in plants. We would like to see 95%,” says Joshi. “So we are working on metabolic engineering methods to enhance the levels of enzymes involved in these reactions in the plant to get maximum yield,” he says.

The study is reported in the journal Nature Biotechnology.

(Vgl. Meldung vom 2002-04-10.)

Source: www.betterhumans.com vom 2003-12-18.

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