Unveiling the molecular mechanism of mitochondrial remodelling in the blood stages of the malaria parasite Plasmodium falciparum.

• Applicant: Dr. Juliane Saßmannshausen
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558306028

The oxidative phosphorylation (OXPHOS) complexes of apicomplexan parasites exhibit a highly extraordinary architecture and composition due to the presence of phylum-specific subunits and extensions. Despite their critical role in the proliferation of Plasmodium falciparum, the causative agent of malaria tropica, and as an important drug target, the functions of the unique plasmodial OXPHOS complexes throughout the life cycle of the parasite are poorly understood and their structures have not been determined. During the stage transition from asexual blood stages (ABS) to gametocytes (GC), the expression of the complexes is strongly increased, associated with a metabolic switch to OXPHOS in GCs and accompanied by a unique stage-specific remodelling of the mitochondrion, mainly affecting the cristae, which is critical for GC development. However, the molecular mechanism underlying the process of mitochondrial remodelling is not understood. We hypothesize, that the mitochondrial remodelling during P. falciparum GC development relies on interactions of the enigmatic parasite-specific complex subunits, allowing a stage-specific oligomerization of the ATP synthase (ATPS) and the assembly of respiratory supercomplexes (SC), leading to membrane bending and the formation of cristae structures within the mitochondrion of GC, thereby enabling stage progression and transmission to the mosquito. To experimentally validate our hypothesis, we will use state-of-the-art structural biology methods to characterize the dynamic assembly of the ATPS and respiratory SC in-situ by performing a cryo-tomographic comparison of ABS and GC stage mitochondria. Specifically, alterations in the mitochondrial surface area between ABS and GC will be quantified, while subtomogram averaging will visualize the spatial localization of the complexes within the mitochondria. The proposed experimental setup will define the differential arrangement of the essential OXPHOS complexes in the inner mitochondrial membrane of ABS and GC and answer the questions why no cristae are formed in the ABS and what changes in the spatial arrangement, assembly state or oligomeric assembly occur in GC that led to cristae shaping. A stage-resolved model of cristae biogenesis in P. falciparum will be generated, which will enable the subsequent functional analysis of the complex components by providing novel structural insights. The generation of subunit knockout or truncation mutants that specifically interfere with the assembly of OXPHOS oligomers, while leaving the resulting monomeric OXPHOS complexes functionally intact, will additionally allow us to probe the function of the secondarily acquired supernumerary subunits in the unique mitochondrial remodelling step. Overall, the findings of this project will break new ground by creating a first direct link between OXPHOS complex structure, mitochondrial remodelling, and parasite viability and proliferation.

• DFG Programme: WBP Fellowship
• International Connection: Finland
• Host: Dr. Alexander Mühleip