Biology subjects

Bisio, H.

Publications and source records attributed to Bisio, H..

3 recordsLinked to original sources

bioRxiv2023

Knockout of GMC-oxidoreductase genes reveals functional redundancy in mimivirus

The mimivirus 1.2Mb genome was shown to be organized into a nucleocapsid-like genomic fiber encased in the nucleoid compartment inside the icosahedral capsid (1). The genomic fiber protein shell is composed of a mixture of two GMC-oxidoreductase paralogs, one of them being the main component of the glycosylated layer of fibrils at the surface of the virion (2). In this study, we determined the effect of the deletion of each of the corresponding genes on the genomic fiber and the layer of surface fibrils. First, we deleted the GMC-oxidoreductase the most abundant in the genomic fiber, and determined its structure and composition in the mutant. As expected, it was composed of the second GMC-oxidoreductase and contained 5- and 6-start helices similar to the wild-type fiber. This result led us to propose a model explaining their coexistence. Then, we deleted the GMC-oxidoreductase the most abundant in the layer of fibrils to analyze its protein composition in the mutant. Second, we showed that the fitness of single mutants and the double mutant were not decreased compared to the wild-type viruses in laboratory conditions. Third, we determined that deleting the GMC-oxidoreductase genes did not impact the glycosylation or the glycan composition of the layer of surface fibrils, despite modifying their protein composition. Since the glycosylation machinery and glycan composition of members of different clades are different (3, 4), we expanded the analysis of the protein composition of the layer of fibrils to members of the B and C clades and showed that it was different among the three clades and even among isolates within the same clade. Taken together, the results obtained on two distinct central processes (genome packaging and virion coating) illustrate an unexpected functional redundancy in members of the family Mimiviridae, suggesting this may be the major evolutionary force behind their giant genomes. One-Sentence SummaryFunctional redundancy preserves mimivirus genomic fiber and layer of fibrils formation.

microbiology↗

bioRxiv2022

Evolution of giant pandoravirus from small icosahedral viruses revealed by CRISPR/Cas9

Giant viruses (GVs) are a hotspot of unresolved controversies since their discovery, including the definition of "Virus" and the existence of a fourth domain of life1-3. While increasing knowledge of genome diversity has accumulated4, functional genomics was largely neglected. Here, we describe an experimental framework to genetically modify nuclear GVs and its host Acanthamoeba castellanii using CRISPR/Cas9, allowing us to uncover the evolution from small icosahedral viruses to amphora-shaped GVs. Ablation of the icosahedral major capsid protein in the evolutionary intermediate mollivirus highlights a stepwise transition in virion shape and size. We additionally demonstrate the existence of a reduced core essential genome in pandoravirus, reminiscent of their proposed smaller ancestors. Genetic expansion led to increased genome robustness, indicating selective pressures for adaptation to uncertain environments. Overall, we introduce new tools for manipulation of the unexplored genome of nuclear GVs and demonstrate that viral gigantism can arise as an emerging trait.

microbiology↗

bioRxiv2021

Toxoplasma gondii phosphatidylserine flippase complex ATP2B-CDC50.4 critically participates in microneme exocytosis

Regulated microneme secretion governs motility, host cell invasion and egress in the obligate intracellular apicomplexans. Intracellular calcium oscillations and phospholipid dynamics critically regulate micronemes exocytosis. Despite its importance for the lytic cycle of these parasites, molecular mechanistic details about exocytosis are still missing. Some members of the P4-ATPases act as flippases, changing the phospholipid distribution by translocation from the outer to the inner leaflet of the membrane. Here, the localization and function of the repertoire of P4-ATPases was investigated across the lytic cycle of Toxoplasma gondii. Of relevance, ATP2B and the non-catalytic subunit cell division control protein 50.4 (CDC50.4) form a stable heterocomplex at the parasite plasma membrane, essential for microneme exocytosis. This complex is responsible for flipping phosphatidylserine (PS), which presumably acts as a lipid mediator for the organelle fusion with the plasma membrane. DOC2.1, a previously described key egress and invasion factor, is shown here to be affected in its function in egress upon mutation on residues putatively involved in calcium binding. This study points toward the importance of PS in microneme exocytosis and unveils subtle differences in the signaling cascades leading to organelle secretion between intracellular and extracellular parasites to ensure egress and invasion, respectively. Author SummaryBiological membranes display diverse functions, including membrane fusion, which are conferred by a defined composition and organization of proteins and lipids. Apicomplexan parasites possess specialized secretory organelles (micronemes), implicated in motility, invasion and egress from host cells. Microneme exocytosis is already known to depends on phosphatidic acid for its fusion with the plasma membrane. Here we identify a type P4-ATPase and its CDC50 chaperone (ATP2B-CDC50.4) that act as flippase and contribute to the enrichment of phosphatidylserine (PS) in the inner leaflet of the parasite plasma membrane. PS and the previously described C2-containing protein DOC2.1 differentially participate in microneme exocytosis in the context of environmental changes. Overall, our results shed light on the importance membrane homeostasis and lipid composition in controlling microneme secretion.

cell biology↗