Prof.Dr. Carmen Faso

Clathrin, a key protein complex involved in membrane trafficking, is conserved across the diversity of eukaryotes. In this project, we study its function in the intestinal parasite Giardia lamblia. This unicellular organism has a highly reduced and divergent cellular machinery, compared to well-studied model organisms, raising questions like how essential processes can be conserved in this context. We combine fluorescence microscopy, ultrastructure expansion microscopy (U-ExM), and cross-linking mass spectrometry with simple computational structural modelling (AlphaFold) to analyze the organization of Giardia clathrin and its interactors at unique endocytic organelles called peripheral endocytic compartments. By comparing these structures to those in other eukaryotes, we gain insights into the evolutionary cell biology of clathrin-mediated endocytosis.

Membranes create distinct cellular compartments by separating specific chemical environments, and their controlled fusion is essential for maintaining cellular functionality. SNARE proteins play a central role in intracellular trafficking in eukaryotic organsims by mediating membrane fusion events. In Giardia lamblia, peripheral endocytic compartments (PECs) mark the parasite–host interface and are essential for both endocytic and exocytic pathways. We are studying a quartet of SNARE proteins and their presumed roles in endo- and exocytosis to advance our understanding of membrane trafficking mechanisms in single-celled parasites.

Parasitism often involves extreme adaptations that promote host infection and colonization while enabling avoidance of mechanical and immune-mediated clearance. The evolution of such an extreme lifestyle likely required major molecular innovations, including changes in protein localization, organelle composition, and endomembrane system dynamics. Giardia lamblia represents an especially striking example: its life cycle alternates between two different environments, the environmentally resistant cyst and the actively feeding, host-associated trophozoite.  In Giardia, the specific proteomic and organellar modifications that support the transition from the cyst stage to the trophozoite stage remain poorly understood. With the support of the Swiss National Science Foundation (SNSF) and the Formas – the Swedish Research Council for Sustainable Development, we are investigating COPI/COPII-associated proteins and how they may regulate the encystation process in Giardia by combining spatial proteomics datasets with CRISPR/Cas9-based functional validation.

Endocytic trafficking is a conserved molecular process in eukaryotes, yet it remains poorly characterized in the intestinal parasite Giardia lamblia. The parasite possesses a highly divergent endocytic uptake system, including a non-canonical form of clathrin-mediated endocytosis. The aim of this project is to assess the degree of functional divergence of Giardias clathrin assemblies relative to the canonical protein. To accomplish this, cross-species functional complementation assays combined with fluorescent microscopy will be employed to investigate clathrin behavior in both divergent and canonical cellular contexts.