Biology subjects

Arrizabalaga, G.

Publications and source records attributed to Arrizabalaga, G..

2 recordsLinked to original sources

bioRxiv2019

The secreted acid phosphatase domain-containing GRA44 from Toxoplasma gondii is required for C-myc induction in infected cells

During host cell invasion, the eukaryotic pathogen Toxoplasma gondii forms a parsitophorous vacuole to safely reside within, while partitioned from host cell defense mechanisms. From within this safe niche parasites sabotage multiple host cell systems including gene expression, apoptosis and intracellular immune recognition by secreting a large arsenal of effector proteins. Many parasite proteins studied for active host cell manipulative interactions have been kinases. Translocation of effectors from the parasitophorous vacuole into the host cell is mediated by a putative translocon complex, which includes proteins MYR1, MYR2, and MYR3. Whether other proteins are involved in the structure or regulation of this putative translocon is not known. We have discovered that the secreted protein GRA44, which contains a putative acid phosphatase domain, interacts with members of this complex and is required for host cell effects downstream of effector secretion. We have determined GRA44 is processed in a region with homology to sequences targeted by protozoan proteases of the secretory pathway and that both major cleavage fragments are secreted into the parasitophorous vacuole. Immunoprecipitation experiments showed that GRA44 interacts with a large number of secreted proteins included MYR1. Importantly, conditional knockdown of GRA44 resulted in a lack of host cell cMyc upregulation, which mimics the phenotype seen when members of the translocon complex are genetically disrupted. Thus, the putative acid phosphatase GRA44 is crucial for host cell alterations during Toxoplasma infection and is associated with the translocon complex which Toxoplasma relies upon for success as an intracellular pathogen. IMPORTANCEApproximately one third of humans are infected with the parasite Toxoplasma gondii. Toxoplasma infections can lead to severe disease in those with a compromised or suppressed immune system. Additionally, infections during pregnancy present a significant health risk to the developing fetus. Drugs that target this parasite are limited, have significant side effects, and do not target all disease stages. Thus, a thorough understanding of how the parasite propagates within a host is critical in the discovery of novel therapeutic targets. To replicate Toxoplasma requires to enter the cells of the infected organism. In order to survive the environment inside a cell, Toxoplasma secretes a large repertoire of proteins, which hijack a number of important cellular functions. How these Toxoplasma proteins move from the parasite into the host cell is not well understood. Our work shows that the putative phosphatase GRA44 is part of a protein complex responsible for this process.

microbiology↗

bioRxiv2019

Identification of Fis1 interactors in Toxoplasma gondii reveals a novel protein required for peripheral distribution of the mitochondrion.

Toxoplasma gondiis singular mitochondrion is very dynamic and undergoes morphological changes throughout the parasites life cycle. During parasite division, the mitochondrion elongates, enters the daughter cells just prior to cytokinesis and undergoes fission. Extensive morphological changes also occur as the parasite transitions from the intracellular to the extracellular environment. We show that treatment with the ionophore monensin causes reversible constriction of the mitochondrial outer membrane, and that this effect depends on the function of the fission related protein Fis1. We also observed that mislocalization of the endogenous Fis1 causes a dominant negative effect that affects the morphology of the mitochondrion. As this suggests Fis1 interacts with proteins critical for maintenance of mitochondrial structure, we performed various protein interaction trap screens. In this manner we identified a novel outer mitochondrial membrane protein, LMF1, which is essential for positioning of the mitochondrion in intracellular parasites. Normally, while inside a host cell, the parasite mitochondrion is maintained in a lasso shape that stretches around the parasite periphery where it has regions of coupling with the parasite pellicle, suggesting the presence of membrane contact sites. In intracellular parasites lacking LMF1 the mitochondrion is retracted away from the pellicle and instead is collapsed, as only normally seen in extracellular parasites. We show that this phenotype is associated with defects in parasite fitness and mitochondrial segregation. Thus, LMF1 is necessary for mitochondrial association with the parasite pellicle during intracellular growth and proper mitochondrial morphology is a prerequisite for mitochondrial division.\n\nIMPORTANCEToxoplasma gondii is an opportunistic pathogen that can cause devastating tissue damage in the immunocompromised and the congenitally infected. Current therapies are not effective against all life stages of the parasite and many cause toxic effects. The single mitochondrion of this parasite is a validated drug target and it changes its shape throughout its life cycle. When the parasite is inside of a cell, the mitochondrion adopts a lasso shape that lies in close proximity to the pellicle. The functional significance of this morphology is not understood nor are the proteins involved currently known. We have identified a protein that is required for proper mitochondrial positioning at the periphery and that likely plays a role in tethering this organelle. Loss of this protein results in dramatic changes to the mitochondrial morphology and significant parasite division and propagation defects. Our results give important insight into the molecular mechanisms regulating mitochondrial morphology.

microbiology↗