Laboratory of Functional Biology of Protists
African trypanosomes (T. brucei brucei, T. congolense, T. vivax), the model organisms of our laboratory, are extracellular parasites that, as the causative agents of African trypanosomiases, pose an enormous medical burden to humans and livestock and have a devastating impact on the economy. These deadly parasites undergo a complex life cycle between their mammalian hosts and insect vectors and face strikingly different environments with varying temperatures, pH, nutrients, immune responses etc.
In order to infect the host, replicate in the host environment, and differentiate into a transmissible life cycle form, the parasite's metabolism must rapidly adapt to the various nutrients provided by the host environment.
We focus on the single mitochondrion of the parasite, which undergoes one of the most extreme metabolic reorganizations known to date. From amino acid oxidation fueling oxidative phosphorylation to aerobic glycolysis, from fully developed cristae-containing reticulated mitochondrion to a single tubular organelle, from ATP-producing organelle to ATP-consuming organelle.
Our goal is to understand what signals (extracellular and intracellular) drive the metabolic remodeling of the parasite and the ultrastructural changes of the mitochondria and what are the molecular mechanisms behind them.
There are two important outcomes of our work. First, our findings can help in drug development. Second, our knowledge can shed light on the basic molecular processes that govern metabolic remodeling during cellular differentiation of all eukaryotic cells, including human stem cells, primary immune cells, and cancer cells.
MitoSignal: Determining signaling mechanisms that drive cellular differentiation of Trypanosoma brucei
Mitochondria perform three essential functions: ATP production, metabolite synthesis and cellular signaling. These signals, communicating the bioenergetic and biosynthetic fitness of the organelle to the nucleus, play a powerful role in determining cellular fate.
Our lab focuses on incorporation of mitochondrial reactive oxygen species (mROS) in cellular signaling. We utilize the unicellular parasites, Trypanosoma brucei and T. congolense, as simplified but elegant models to define mROS-driven cellular differentiation. As these protists undergo programmed development between several distinct life cycle forms, there are striking changes to the structure and physiology of their single mitochondrion that manifest in elevated ROS levels. Importantly, we demonstrated that these ROS molecules are essential for the developmental progression of the parasite. Employing these well-chosen models and combining next-generation biosensors, advanced bioenergetic methods, redox proteomics and a CRISPR/Cas9 genetic screen, we are answering the following fundamental questions: Does mROS drive Trypanosoma cellular differentiation? What molecular processes are responsible for the elevated mROS levels during differentiation? How is the redox signal propagated to the rest of the cell? Our research aspires to unravel the fundamental mechanisms underlying the intricate communication between mitochondria and the rest of the cell, featuring cellular hallmarks of cell fate decision.
T. brucei bloodstream form mitochondrion: a key player in the parasite bioenergetics and metabolism
For the last 50 years, the bioenergetic dogma of the infectious stage of the human pathogen Trypanosoma brucei has been that the mitochondrion is an ATP-consuming organelle and that glycolysis is the sole source of cellular ATP.
We have shown that under certain environmental or genetic conditions, the mitochondrion of the bloodstream is capable of producing ATP via the substrate phosphorylation pathway.
Our discovery opens new opportunities to study mitochondrial metabolic pathways to redefine the metabolic role of the parasite mitochondrion.
We hope that our findings will open new opportunities for drug development and explain the molecular mechanisms behind the mode of action and drug resistance of commonly used drugs that accumulate in the parasite mitochondrion.
The role of ATP synthase structure in the biogenesis and bioenergetics
Mitochondrial cristae are inner membrane convolutions where protein factories responsible for bioenergy conversion reside. The cristae exhibit extremely large variability in their ultrastructure, except for one common attribute - the presence of ATP synthase dimer rows at the crista ridges. Little is known about the role of these arrays in cristae structure and mitochondrial bioenergetics. However, Trypanosoma brucei is an excellent model system as the singular mitochondrion of the digenetic parasite is drastically remodeled structurally and metabolically as it progresses through a complex life cycle. Notably, the highly branched, cristae-containing and ATP-producing mitochondrion transitions to a streamlined tubular, cristae-lacking and ATP-consuming organelle. Combining traditional biochemical methods with state-of-art structural approaches (single-particle cryo-EM), we solved the ATP synthase dimer structure, identified a dimer-specific subunit and explored its role in cristae shaping.
Now we aim to decipher the role of ATP synthase dimers in mitochondrial bioenergetics and biogenesis during the parasite differentiation.
Acyclic nucleaoside phosphonates as potent nhibitors of purine salvage pathway enzymes
The purine salvage pathway (PSP) in unicellular parasites complies with key requirements for essentiality, potential druggability, availability of in vitro assays, and availability of structural information of target enzymes. In contrast to their mammalian hosts, trypanosomatids (as well as malaria parasites) lost their ability to synthesize nucleoside monophosphates de novo and they rely entirely on the acquisition of purines from the host environment. Recently several enzymes of the PSP (i.e., GMP synthase, hypoxanthine-guanine-(xanthine) phosphoribosyltransferase HG(X)PRT) have been experimentally validated as potential therapeutic targets. It has also been shown that selected prodrugs of potent acyclic nucleoside phosphonates (ANPs), inhibitors of HGXPRT and HGPRT, block the growth of above-mentioned parasites.
The current study focused on Trypanosoma brucei (Tbr) purine salvage pathway (PSP). To complement our preliminary studies on key PSP enzymes, 6-oxopurine PRTs and their inhibitors (ANPs), we decided to add adenine PRT (APRT) to the studied portfolio of enzymes and study APRT side by side to 6-oxopurine PRTs.