Biology subjects

Faso, C.

Publications and source records attributed to Faso, C..

6 recordsLinked to original sources

bioRxiv2026

The N terminus of Alpha-1 Giardin, a parasitic annexin orthologue, is essential for oligomerization and lipid-binding activity

Annexins are Ca{superscript 2}- and membrane-binding proteins conserved across eukaryotes and involved in diverse membrane-associated processes, including unconventional protein secretion (UPS). In the intestinal parasite Giardia lamblia, annexins are represented by a family of 21 proteins termed alpha-giardins (Gs), all of which lack classical signal peptides yet are detected at the parasite surface and in the secretome. Here, we present a comprehensive functional analysis of Gs, with a particular focus on 1-giardin (1G), a leading vaccine candidate against giardiasis and a putative virulence-associated UPS substrate. We show that Gs localize to peripheral endocytic compartments (PECs), specialized endo-lysosomal organelles implicated in protein release, and engage in multiprotein complexes enriched in UPS substrates. Using lipid-binding assays, cross-linking mass spectrometry, and structural modelling, we define conserved and divergent features of G membrane interactions. Focusing on 1G, we combine site-directed mutagenesis, confocal microscopy, and mass photometry to demonstrate a critical role for its short N-terminal region in oligomerization and membrane association. Integration of these data with molecular dynamics simulations reveals how 1G oligomeric state and membrane occupancy are regulated at PEC membranes. Together, our findings establish a mechanistic framework for annexin-mediated UPS in Giardia and provide structural insights relevant to parasite virulence and vaccine development.

cell biology↗

bioRxiv2025

The ARF regulatory GTPase in Giardia intestinalis is associated with vesicle formation and membrane fusion machinery at non-canonical endosomal compartments

The intestinal parasite Giardia intestinalis, the causative agent of the globally distributed diarrheal disease Giardiasis, is one of the few genetically tractable members of the phylum Fornicata, which includes both parasitic and free-living species. The diversity of membrane traffic machinery in this lineage is of special interest in relation to the evolution of parasitism and the emergence of specialized organelles as possible adaptations to parasitism. Here, we performed a functional characterization of the ARF family of regulatory GTPases and their regulators in Giardia traffic, including three ARF paralogues, one ARF GAP and one ARF GEF. Using a combination of bioinformatic tools, protein network discovery and validation, and confocal light microscopy, we show that the Giardia ARF complement studied here is robustly associated with peripheral endocytic compartments (PECs), essential feeding organelles that are unique to Giardia parasites. Intersection of the interactomes of this ARF complement with previously published data for PECs-proteins (including membrane adaptors, predicted retromer subunits and SNAREs), revealed a complex crosstalk between the ARF complement and several membrane traffic processes.

cell biology↗

bioRxiv2022

A core UPS molecular complement implicates unique endocytic compartments at the parasite-host interface in Giardia lamblia

Unconventional protein secretion (UPS) plays important roles in processes for the survival of the cell and whole organisms. In contrast to canonical secretory routes, UPS does not generally require secretory signal sequences and often bypasses secretory compartments such as the ER and the Golgi apparatus. Giardia lamblia is a protozoan parasite of global medical importance and reduced subcellular complexity known to release several proteins, some of them virulence factors, without canonical secretory signals, thus implicating UPS at the parasite-host interface. No dedicated machinery nor mechanism(s) for UPS in Giardia are currently known, although speculations on unique endocytic Giardia compartments called PV/PECs have been put forth. To begin to address the question of whether PV/PECs are implicated in virulence-associated UPS and to define the composition of molecular machinery involved in release of confirmed and putative virulence factors, in this study we employed affinity purification and mass spectrometry coupled to microscopy-based subcellular localization and signal correlation quantification techniques to investigate protein complexes of eleven reported unconventionally-secreted putative and confirmed virulence factors, all predicted to be cytosolic. A subset of selected putative and confirmed virulence factors, along with their interaction partners, unequivocally associate to the surface of PV/PECs. Extended and validated interactomes point to a core PV/PECs-associated UPS machinery, which includes uncharacterized and Giardia-specific coiled-coil proteins and NEK kinases. Finally, a specific subset of the alpha-giardin protein family was invariably found enriched in all PV/PECs-associated protein interactomes, highlighting a previously unappreciated role for these proteins at PV/PECs and in UPS. Taken together, our results provide the first characterization of a virulence-associated UPS protein complex in Giardia lamblia at PVs/PECs, suggesting a novel link between these primarily endocytic and feeding organelles and UPS at the parasite-host interface.

cell biology↗

bioRxiv2022

Combined nanometric and phylogenetic analysis of unique endocytic compartments in Giardia lamblia sheds light on the evolution of endocytosis in Fornicata

Giardia lamblia, a parasitic protist of the metamonada supergroup, has evolved one of the most diverged endocytic compartment systems investigated so far. Peripheral endocytic compartments, currently known as peripheral vesicles or vacuoles (PVs), perform bulk uptake of fluid phase material which is then digested and sorted either to the cell cytosol or back to the extracellular space. Here, we present a quantitative morphological characterization of these organelles using volumetric electron microscopy and super-resolution microscopy (SRM). We defined a morphological classification for the heterogenous population of PVs and performed a comparative analysis of PVs and endosome-like organelles in representatives of phylogenetically-related taxa, Spironucleus spp. and Tritrichomonas foetus. To investigate the as-yet insufficiently understood connection between PVs and clathrin assemblies in G. lamblia, we further performed an in-depth search for two key elements of the endocytic machinery, clathrin heavy chain (CHC) and clathrin light chain (CLC) across different lineages in Metamonada. Our data point to the loss of a bona fide CLC in the last Fornicata common ancestor (LFCA) with the emergence of a protein analogous to CLC (GlACLC) in the Giardia genus. Taken together, this provides the first comprehensive nanometric view of Giardias endocytic system architecture and sheds light on the evolution of GLACLC analogues in the Fornicata supergroup and, specific to Giardia, as a possible adaptation to the formation and maintenance of stable clathrin assemblies at PVs.

cell biology↗

bioRxiv2021

Unexpected organellar locations of ESCRT machinery in Giardia intestinalis and complex evolutionary dynamics spanning the transition to parasitism in the lineage Fornicata

Comparing a parasitic lineage to its free-living relatives is a powerful way to understand how the evolutionary transition to parasitism occurred. Giardia intestinalis (Fornicata) is a leading cause of gastrointestinal disease world-wide and is famous for its unusual complement of cellular compartments, such as having peripheral vacuoles instead of typical endosomal compartments. Endocytosis plays an important role in Giardias pathogenesis. Endosomal sorting complexes required for transport (ESCRT) are membrane-deforming proteins associated with the late endosome/multivesicular body (MVB). MVBs are ill-defined in G. intestinalis and roles for identified ESCRT-related proteins are not fully understood in the context of its unique endocytic system. Furthermore, components thought to be required for full ESCRT functionality have not yet been documented in this species. We used genomic and transcriptomic data from several Fornicata species to clarify the evolutionary genome streamlining observed in Giardia, as well as to detect any divergent orthologs of the Fornicata ESCRT subunits. We observed differences in the ESCRT machinery complement between Giardia strains. Microscopy-based investigations of key components of ESCRT machinery such as GiVPS36and GiVPS25 link them to peripheral vacuoles, highlighting these organelles as simplified MVB equivalents. Unexpectedly, we show ESCRT components associated with the Endoplasmic Reticulum, and for the first time, mitosomes. Finally, we identified the rare ESCRT component CHMP7 in several fornicate representatives, including Giardia, and show that contrary to current understanding, CHMP7 evolved from a gene fusion of VPS25 and SNF7 domains, prior to the last eukaryotic common ancestor, over 1.5 billion years ago. Our findings show that ESCRT machinery in G. intestinalis is far more varied and complete than previously thought, and associating to multiple cellular locations and presenting changes in ESCRT complement which pre-date adoption of a parasitic lifestyle.

evolutionary biology↗

bioRxiv2019

Phosphoinositide-binding proteins mark, shape and functionally modulate highly-diverged endocytic compartments in the parasitic protist Giardia lamblia

Phosphorylated derivatives of phosphatidylinositol (PIPs), are key membrane lipid residues involved in clathrin-mediated endocytosis (CME). CME relies on PI(4,5)P2 to mark endocytic sites at the plasma membrane (PM) associated to clathrin-coated vesicle (CCV) formation. The highly diverged parasitic protist Giardia lamblia presents disordered and static clathrin assemblies at PM invaginations, contacting specialized endocytic organelles called peripheral vacuoles (PVs). The role for clathrin assemblies in fluid phase uptake and their link to internal membranes via PIP-binding adaptors is unknown.\n\nHere we provide evidence for a robust link between clathrin assemblies and fluid-phase uptake in G. lamblia mediated by proteins carrying predicted PX, FYVE and NECAP1 PIP-binding modules. We show that chemical and genetic perturbation of PIP-residue binding and turnover elicits novel uptake and organelle-morphology phenotypes. A combination of co-immunoprecipitation and in silico annotation techniques expands the initial PIP-binding network with addition of new members. Our data indicate that, despite the partial conservation of lipid markers and protein cohorts known to play important roles in dynamic endocytic events in well-characterized model systems, the Giardia lineage presents a strikingly divergent clathrin-centered network. This includes several PIP-binding modules, often associated to domains of currently unknown function that shape and modulate fluid-phase uptake at PVs.

microbiology↗