Trypanosomes are parasitic organisms responsible for severe diseases in both humans and animals, including Human African Trypanosomiasis (commonly known as sleeping sickness), Chagas disease, and Nagana affecting cattle. The World Health Organization indicates that continuous efforts to control these diseases have led to a decrease in sleeping sickness cases, yet millions are still estimated to suffer from Chagas disease. Diagnosing and treating these diseases is complex, and as of now, there is no effective vaccine available for these neglected tropical diseases.
Trypanosomes are parasites responsible for serious diseases in humans and animals, such as sleeping sickness (Human African Trypanosomiasis), Chagas disease, and Nagana affecting livestock. The World Health Organization reports that ongoing control measures have reduced sleeping sickness cases, but millions are believed to still be affected by Chagas disease. The challenges of diagnosing and treating these conditions remain, and currently, an effective vaccine is yet to be developed for these neglected tropical diseases.
A recent study led by the Kowalinski group at EMBL Grenoble has detailed the structure of a significant protein complex in trypanosomes, which may lead to new drug discoveries in the future.
At present, trypanosome-transmitting insect species are predominantly located in the Southern Hemisphere. However, climate change may facilitate the global transmission of insect-borne diseases, making it increasingly crucial to understand the biology of these parasites.
Trypanosomes, much like other organisms, transcribe their DNA into messenger RNAs (mRNAs). These mRNAs act as instructions that guide the cell in producing proteins necessary for essential biological functions, including the infection process within a host.
Both humans and trypanosomes belong to the eukaryotic group of organisms, meaning they have their DNA enclosed within a nucleus. In eukaryotes, mRNAs undergo significant processing before their instructions can be utilized by the cell. Given the notable differences in mRNA processing between humans and trypanosomes, gaining a clearer understanding of these molecular processes is essential for creating drugs that can specifically target RNA processing in the parasite without harming human cells.
In their latest research published in Nature Communications, the Kowalinski group investigated the nuclear cap-binding complex, which is key to the functionality of trypanosomes as it binds to all of the parasites’ mRNAs. This complex is crucial for proper mRNA processing and the parasite’s survival. The researchers uncovered significant differences between the nuclear cap-binding complexes of trypanosomes and humans, indicating it could be a viable target for drug development.
Different pathways
The nuclear cap-binding complex plays an crucial role in RNA metabolism in all eukaryotic organisms. It binds to RNA early in its synthesis process, and other components of the cellular machinery then interact with the RNA via this complex to guide it to further processing stages or alternate locations within the cell.
Unlike the human version, which consists of two subunits, the trypanosome nuclear cap-binding complex is made up of four subunits. The functions of three of these subunits were not previously understood, which ignited the curiosity of the Kowalinski team.
Their findings indicated that this complex comprises two lobes—one resembling the human complex and a second connected by a highly flexible protein.
“One major challenge in studying this complex was its flexibility,” explained Harald Bernhard, a former PhD candidate in the Kowalinski group and the study’s lead author. “I initially used cryo-electron microscopy (cryo-EM) to create a structure of the complex, but the flexible sections remained unresolved in our data. Consequently, we shifted to small-angle X-ray scattering.” The team leveraged X-ray beams from the European Synchrotron Radiation Facility in Grenoble to evaluate the flexible components of the complex.
Typically, the ends of mRNA molecules are chemically modified, but in trypanosomes, this ‘cap’ is heavily modified, featuring significantly more alterations compared to other organisms. “Because trypanosomes have a distinctive RNA cap structure, we were intrigued by how the nuclear cap-binding complex interacts with this cap as well as the RNA molecule itself,” noted Eva Kowalinski, the group leader at EMBL Grenoble and principal investigator on the study.
The researchers utilized their cryo-EM structures to illuminate the interaction between the nuclear cap-binding complex and the RNA cap structure. Binding assays also pointed to a second, novel binding site for RNA within the complex. “We investigated this observation and discovered that one of the flexibly linked subunits, previously thought to be functionless, specifically binds to double-stranded RNAs,” described Hana Petrzilkova, a research assistant in Kowalinski’s lab who contributed to this publication.
A potential drug target and future studies
Considering the essential role of the cap-binding complex for the parasite and its notable differences from the human equivalent, it presents a possible target for future drug development.
“A PhD student in my group is currently exploring this avenue,” Kowalinski added. “This project is backed by EMBL and the local University of Grenoble Alpes through the ‘Grenoble Attractiveness and Excellences Initiative,’ which is funded by the France 2030 framework of the French National Research Agency ANR.”
Furthermore, the insights gained from studying the nuclear cap-binding complex will lay the groundwork for a comprehensive understanding of RNA biogenesis and processing in Trypanosoma brucei (T. brucei). Beyond its implications for human and animal health, T. brucei serves as a model organism for researching the roots of eukaryotic life and evolution.
Kowalinski has also recently secured ERC funding to investigate mRNA processing in trypanosomes through a mechanism known as trans-splicing. This mechanism shows promise as a molecular tool for RNA editing—a novel approach to gene therapy that is currently being evaluated in various clinical trials.
