New drug shows promise against toxoplasmosis

Overview: Using AI-generated information, researchers developed a new drug against toxoplasmosis.

Source: University of Kentucky

Findings of a new study from the University of Kentucky College of Medicine published in the Journal of Biological Chemistry May 28 may lead to a new treatment against Toxoplasma gondii, the parasite that causes toxoplasmosis.

The Centers for Disease Control and Prevention report that an estimated 40 million people in the US carry the parasite T. gondii, but very few have symptoms because the immune system usually stops the parasite from causing disease. However, toxoplasmosis can have serious consequences for women newly infected during pregnancy and for anyone with a compromised immune system.

Those who have severe toxoplasmosis may harbor a cyst version of the parasite in brain and muscle tissue. These cysts are responsible for causing serious illness, especially in people who are immunocompromised.

The labs of Matthew Gentry, Ph.D., and Craig Vander Kooi, Ph.D., in the Department of Molecular and Cellular Biochemistry, Anthony Sinai, Ph.D., in the Department of Microbiology, Immunology, and Molecular Genetics, and Zhong- Yin Zhang, Ph.D., of the Purdue Institute for Drug Discovery, teamed up to develop a drug that targets the cyst form of the parasite.

In previous research, Gentry identified an enzyme in T. gondii called TgLaforin, which he hypothesized was critical in allowing the parasite to access energy from a carbohydrate storage molecule. The team developed a new drug that inhibits TgLaforin with the aim of preventing enzymes from accessing and supplying energy to the parasite.

While there are FDA-approved medications to treat the symptoms of toxoplasmosis, there are no current therapies targeting the cyst form of the parasite.

The new discovery was made possible thanks to the multidisciplinary collaboration of experts from the four labs, Gentry says.

Robert Murphy, Ph.D., a member of the Gentry and Sinai labs, conducted initial experiments that characterized TgLaforin and provided a baseline for understanding the enzyme’s function.

Tiantian Chen, a graduate student in Vander Kooi’s lab, generated models of TgLaforin using a new program called AlphaFold2, an artificial intelligence algorithm that provides valuable insights into research. Chen generated models that visualized the enzyme that showed that TgLaforin was a unique and possible drug target.

Those who have severe toxoplasmosis may harbor a cyst version of the parasite in brain and muscle tissue. Image is in the public domain

Jianping Lin, Ph.D., a postdoc in Zhang’s lab, then used information generated by Murphy and Chen in combination with new chemistry techniques to generate the first version of a future anti-Toxoplasma drug.

“I was excited to find that the drug was effective against TgLaforin in test tubes and that it prevented TgLaforin from exerting its normal activity against a variety of substrates, including carbohydrates,” Murphy said.

Future work from these labs will test the drug for parasites. The team will then attempt to increase potency and selectivity and modify chemical properties to allow for animal studies.

“This study is a great example of what Provost DiPaola consistently promotes with regard to transdisciplinary research,” Gentry said. “This work has been a real team effort and it’s very exciting to see where we take it now.”

About this research news on neuropharmacology and toxoplasmosis

Author: press office
Source: University of Kentucky
Contact: Press Office – University of Kentucky
Image: The image is in the public domain

Original research: Closed access.
“The Toxoplasma glucan phosphatase TgLaforin utilizes a clear functional mechanism that can be exploited by therapeutic inhibitors” by Robert D. Murphy et al. Journal of Biological Chemistry


Abstract

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The Toxoplasma glucan phosphatase TgLaforin utilizes a clear functional mechanism that can be exploited by therapeutic inhibitors

Toxoplasma gondii is an intracellular parasite that generates amylopectin granules (AGs), a polysaccharide associated with bradyzoites that cause chronic T. gondii infection. AGs are hypothesized to act as an essential energy storage molecule enabling the persistence, transmission and reactivation of bradyzoites.

Importantly, reactivation can result in the life-threatening symptoms of toxoplasmosis. T. gondii encodes glucandikinase and glucan phosphatase enzymes that are homologous to the plant and animal enzymes involved in reversible glucan phosphorylation and required for efficient degradation and utilization of polysaccharides.

The structural determinants driving reversible glucan phosphorylation in T. gondii are unclear. Here we define the most important functional aspects of the T. gondii glucan phosphatase TgLaforin (TGME49_205290).

We demonstrate that TgLaforin possesses an atypically spliced ​​carbohydrate-binding module domain.

AlphaFold2 modeling combined with hydrogen-deuterium exchange mass spectrometry and differential scanning fluorimetry also demonstrate the unique structural dynamics of TgLaforin with respect to glucan binding. In addition, we show that TgLaforin forms a phosphatase domain-mediated dimer with dual specificity.

Finally, the different properties of the glucan phosphatase catalytic domain were used to identify a small molecule inhibitor of TgLaforin catalytic activity.

Together, these studies define a clear mechanism of TgLaforin activity, opening a new avenue for T. gondii bradyzoite biology as a therapeutic target.

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