A team has tracked down potential target for sleeping sickness drugs, A research team has found a potential target for new drugs for sleep disease with very bright X-rays.

Scientists have described the detailed spatial structure of vital pathogenic enzymes – the Trypanosoma brucei parasite.

The results provide a possible plan for a drug that specifically blocks this enzyme, killing the parasite.

Sleeping sickness (African trypanosomiasis) is a tropical disease caused by the Trypanosoma brucei parasite and transmitted by the bite of the tsetse fly that inhabits many parts of tropical Africa. In the body, parasites first multiply under the skin, in the blood and in the lymphatic system and then migrate to the central nervous system. If left untreated, this disease is almost always fatal. Research team has tracked down potential target for sleeping sickness drugs.

Even so, sleeping sickness is still considered one of the most important tropical diseases. According to the World Health Organization, more than 60 million people are at risk in sub-Saharan Africa. This disease can spread through war, displacement and migration.

In searching for a possible starting point for pathogenic drugs, the researchers focused on a single cell central enzyme, inosin 5′-monophosphate dehydrogenase (IMPDH). This enzyme is part of the central inventory of each organism and is an attractive drug target because it regulates the concentration of two vital nucleotides in cells: guanosin diphosphate and guanosin triphosphate.

Cells need these nucleotides to conduct energy and build larger structures like the genome. If you stop this cycle, the cell dies.

This enzyme has a type of on / off switch which is activated by binding to the cell molecules themselves. A promising approach is to block this switch with the right molecule. To design such a resistor, the exact spatial structure of the switch must be known. Structural biologists can use X-rays to determine the structure of biomolecules. team has tracked down potential target for sleeping sickness drugs

To do this, they first grow small crystals from biomolecules that produce a typical diffraction pattern when exposed to X-rays.

The structure of the crystal atom and its building blocks, biomolecules, can be calculated from this model.

This approach is often hampered by the instability of most biomolecules in the formation of crystals. And if such crystals can be planted, they are usually very sensitive to high-energy X-rays and are quickly destroyed. Although the structure of many IMP dehydrogenases is known, it is not possible to grow crystals from the enzyme version of Trypanosoma brucei.

The team decided on an alternative method: A group of joint authors, Michael Dushenko from the University of Tübingen, had several insect cells crystallizing biomolecules in them. With cellulose-based crystallization, the same team has broken down another key enzyme from a sleep-sicking pathogen, Cathepsin B, which is also a potential drug target.

It turns out that modified insect cells also produce crystals from dehydrogenase which are now being investigated.

These crystals form small needles with a thickness of about 5,000 millimeters (5 microns) and lengths of up to 70 microns, so they protrude from the producing cells.

Cellulose crystals are so small that very bright X-rays are needed to analyze them. The larger the crystal, the more atoms can spread X-rays, which leads to better diffraction patterns.

Therefore the researchers used the LCLS X-ray laser from the US National SLAC Accelerator Laboratory for analysis.

Although sensitive crystals immediately evaporate, they first create a diffraction pattern from which the structure can be obtained.

The team recorded a diffraction pattern of more than 22,000 microcrystals and was able to calculate the spatial structure of the enzyme with an accuracy of 0.28 million millimeters (nanometers), which is approximately the diameter of an aluminum atom.

The results show not only the exact structure of the enzyme switch, the Bateman region, but also which cell molecules activate the switch and how these so-called factors bind to the enzyme switch.

The switch is controlled by the molecules adenosine triphosphate (ATP) and guanosin monophosphate (GMP). The advantage of our method is not only that we can check the enzyme at room temperature, where the enzyme works naturally, but also that during cellulose crystallization, natural factors that bind to the enzyme.

For example, you might consider building a kind of clothespin to cover the connection points of the two cofactors.

However, the challenge remains to design IMP dehydrogenase inhibitors to block parasitic enzymes, but not human enzymes. If successful, this method can be extended to other pathogens, Researcher explains..

Other parasites have very similar structures and can also be attacked by the corresponding IMP dehydrogenase.

The enzyme is a very attractive drug target such as a fox tapeworm or an agent that causes elephantiasis.


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