scholarly journals A Conserved Apicomplexan Microneme Protein Contributes to Toxoplasma gondii Invasion and Virulence

2014 ◽  
Vol 82 (10) ◽  
pp. 4358-4368 ◽  
Author(s):  
My-Hang Huynh ◽  
Martin J. Boulanger ◽  
Vern B. Carruthers
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Cell Recognition ◽  
Epidermal Growth Factor Domain ◽  
Content Type ◽  
Apicomplexan Parasites ◽  
Epidermal Growth ◽  
The Many ◽  
Host Cell Recognition

ABSTRACTThe obligate intracellular parasiteToxoplasma gondiicritically relies on host cell invasion during infection. Proteins secreted from the apical micronemes are central components for host cell recognition, invasion, egress, and virulence. Although previous work established that the sporozoite protein with an altered thrombospondin repeat (SPATR) is a micronemal protein conserved in other apicomplexan parasites, includingPlasmodium,Neospora, andEimeria, no genetic evidence of its contribution to invasion has been reported. SPATR contains a predicted epidermal growth factor domain and two thrombospondin type 1 repeats, implying a role in host cell recognition. In this study, we assess the contribution ofT. gondiiSPATR (TgSPATR) toT. gondiiinvasion by genetically ablating it and restoring its expression by genetic complementation. Δspatrparasites were ∼50% reduced in invasion compared to parental strains, a defect that was reversed in the complemented strain. In mouse virulence assays, Δspatrparasites were significantly attenuated, with ∼20% of mice surviving infection. Given the conservation of this protein among the Apicomplexa, we assessed whether thePlasmodium falciparumSPATR ortholog (PfSPATR) could complement the absence of the TgSPATR. Although PfSPATR showed correct micronemal localization, it did not reverse the invasion deficiency of Δspatrparasites, because of an apparent failure in secretion. Overall, the results suggest that TgSPATR contributes to invasion and virulence, findings that have implications for the many genera and life stages of apicomplexans that express SPATR.

scholarly journals Two Phosphoglucomutase Paralogs Facilitate Ionophore-Triggered Secretion of the Toxoplasma Micronemes

mSphere ◽  
2017 ◽  
Vol 2 (6) ◽  
Author(s):  
Sudeshna Saha ◽  
Bradley I. Coleman ◽  
Rashmi Dubey ◽  
Ira J. Blader ◽  
Marc-Jan Gubbels
Keyword(s):  
Toxoplasma Gondii ◽  
Phosphatidic Acid ◽  
Host Cell ◽  
Lytic Cycle ◽  
Ionophore A23187 ◽  
Host Cell Invasion ◽  
Content Type ◽  
Apicomplexan Parasites ◽  
Genetic Deletion

ABSTRACT Ca2+-dependent exocytosis is essential for the life cycle of apicomplexan parasites. Toxoplasma gondii harbors a phosphoglucomutase (PGM) ortholog, PRP1, previously associated with Ca2+-dependent microneme secretion. Here it is shown that genetic deletion of either PRP1, its PGM2 ortholog, or both genes is dispensable for the parasite’s lytic cycle, including host cell egress and invasion. Depletion of the proteins abrogated high Ca2+-mediated microneme secretion induced by the ionophore A23187; however, the constitutive and phosphatidic acid-mediated release remained unaffected. Secretion mediated by the former pathway is not essential for tachyzoite survival or acute in vivo infection in the mice. Paralogs of the widely prevalent phosphoglucomutase (PGM) protein called parafusin function in calcium (Ca2+)-mediated exocytosis across eukaryotes. In Toxoplasma gondii, the parafusin-related protein 1 (PRP1) has been associated with Ca2+-dependent microneme organelle secretion required for essential processes like host cell invasion and egress. Using reverse genetics, we observed PRP1 to be dispensable for completion of the lytic cycle, including host cell invasion and egress by the parasite. However, the absence of the gene affected increased microneme release triggered by A23187, a Ca2+ ionophore used to raise the cytoplasmic Ca2+ concentration mimicking the physiological role of Ca2+ during invasion and egress. The basal levels of constitutive microneme release in extracellular parasites and phosphatidic acid-triggered microneme secretion were unaffected in the mutant. The phenotype of the deletion mutant of the second PGM-encoding gene in Toxoplasma, PGM2, was similar to the phenotype of the PRP1 deletion mutant. Furthermore, the ability of the tachyzoites to induce acute infection in the mice remained normal in the absence of both PGM paralogs. Our data thus reveal that the microneme secretion upon high Ca2+ flux is facilitated by the Toxoplasma PGM paralogs, PRP1 and PGM2. However, this protein-mediated release is neither essential for lytic cycle completion nor for acute virulence of the parasite. IMPORTANCE Ca2+-dependent exocytosis is essential for the life cycle of apicomplexan parasites. Toxoplasma gondii harbors a phosphoglucomutase (PGM) ortholog, PRP1, previously associated with Ca2+-dependent microneme secretion. Here it is shown that genetic deletion of either PRP1, its PGM2 ortholog, or both genes is dispensable for the parasite’s lytic cycle, including host cell egress and invasion. Depletion of the proteins abrogated high Ca2+-mediated microneme secretion induced by the ionophore A23187; however, the constitutive and phosphatidic acid-mediated release remained unaffected. Secretion mediated by the former pathway is not essential for tachyzoite survival or acute in vivo infection in the mice.

scholarly journals A Toxoplasma gondii Ortholog of Plasmodium GAMA Contributes to Parasite Attachment and Cell Invasion

mSphere ◽  
2016 ◽  
Vol 1 (1) ◽  
Author(s):  
My-Hang Huynh ◽  
Vern B. Carruthers
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Cell Invasion ◽  
Genetic Evidence ◽  
Specific Role ◽  
Host Cells ◽  
Human Pathogen ◽  
Content Type ◽  
Apicomplexan Parasites ◽  
Adhesive Proteins

ABSTRACT Toxoplasma gondii is a successful human pathogen in the same phylum as malaria-causing Plasmodium parasites. Invasion of a host cell is an essential process that begins with secretion of adhesive proteins onto the parasite surface for attachment and subsequent penetration of the host cell. Conserved invasion proteins likely play roles that were maintained through the divergence of these parasites. Here, we identify a new conserved invasion protein called glycosylphosphatidylinositol-anchored micronemal antigen (GAMA). Tachyzoites lacking TgGAMA were partially impaired in parasite attachment and invasion of host cells, yielding the first genetic evidence of a specific role in parasite entry into host cells. These findings widen our appreciation of the repertoire of conserved proteins that apicomplexan parasites employ for cell invasion. Toxoplasma gondii and its Plasmodium kin share a well-conserved invasion process, including sequential secretion of adhesive molecules for host cell attachment and invasion. However, only a few orthologs have been shown to be important for efficient invasion by both genera. Bioinformatic screening to uncover potential new players in invasion identified a previously unrecognized T. gondii ortholog of Plasmodium glycosylphosphatidylinositol-anchored micronemal antigen (TgGAMA). We show that TgGAMA localizes to the micronemes and is processed into several proteolytic products within the parasite prior to secretion onto the parasite surface during invasion. TgGAMA from parasite lysate bound to several different host cell types in vitro, suggesting a role in parasite attachment. Consistent with this function, tetracycline-regulatable TgGAMA and TgGAMA knockout strains showed significant reductions in host cell invasion at the attachment step, with no defects in any of the other stages of the parasite lytic cycle. Together, the results of this work reveal a new conserved component of the adhesive repertoire of apicomplexan parasites. IMPORTANCE Toxoplasma gondii is a successful human pathogen in the same phylum as malaria-causing Plasmodium parasites. Invasion of a host cell is an essential process that begins with secretion of adhesive proteins onto the parasite surface for attachment and subsequent penetration of the host cell. Conserved invasion proteins likely play roles that were maintained through the divergence of these parasites. Here, we identify a new conserved invasion protein called glycosylphosphatidylinositol-anchored micronemal antigen (GAMA). Tachyzoites lacking TgGAMA were partially impaired in parasite attachment and invasion of host cells, yielding the first genetic evidence of a specific role in parasite entry into host cells. These findings widen our appreciation of the repertoire of conserved proteins that apicomplexan parasites employ for cell invasion.

scholarly journals Atomic resolution insight into host cell recognition by Toxoplasma gondii

2007 ◽  
Vol 26 (11) ◽  
pp. 2808-2820 ◽  
Author(s):  
Tharin M A Blumenschein ◽  
Nikolas Friedrich ◽  
Robert A Childs ◽  
Savvas Saouros ◽  
Elisabeth P Carpenter ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Atomic Resolution ◽  
Cell Recognition ◽  
Host Cell Recognition ◽  
Insight Into

scholarly journals Functional Analysis of Rhomboid Proteases during Toxoplasma Invasion

mBio ◽  
2014 ◽  
Vol 5 (5) ◽  
Author(s):  
Bang Shen ◽  
Jeffrey S. Buguliskis ◽  
Tobie D. Lee ◽  
L. David Sibley
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Cell Invasion ◽  
Gliding Motility ◽  
Surface Proteins ◽  
Host Cell Invasion ◽  
Content Type ◽  
Apicomplexan Parasites ◽  
Transmembrane Segments ◽  
Rhomboid Proteases

ABSTRACT Host cell invasion by Toxoplasma gondii and other apicomplexan parasites requires transmembrane adhesins that mediate binding to receptors on the substrate and host cell to facilitate motility and invasion. Rhomboid proteases (ROMs) are thought to cleave adhesins within their transmembrane segments, thus allowing the parasite to disengage from receptors and completely enter the host cell. To examine the specific roles of individual ROMs during invasion, we generated single, double, and triple knockouts for the three ROMs expressed in T. gondii tachyzoites. Analysis of these mutants demonstrated that ROM4 is the primary protease involved in adhesin processing and host cell invasion, whereas ROM1 or ROM5 plays negligible roles in these processes. Deletion of ROM4 blocked the shedding of adhesins such as MIC2 (microneme protein 2), causing them to accumulate on the surface of extracellular parasites. Increased surface adhesins led to nonproductive attachment, altered gliding motility, impaired moving junction formation, and reduced invasion efficiency. Despite the importance of ROM4 for efficient invasion, mutants lacking all three ROMs were viable and MIC2 was still efficiently removed from the surface of invaded mutant parasites, implying the existence of ROM-independent mechanisms for adhesin removal during invasion. Collectively, these results suggest that although ROM processing of adhesins is not absolutely essential, it is important for efficient host cell invasion by T. gondii. IMPORTANCE Apicomplexan parasites such as Toxoplasma gondii express surface proteins that bind host cell receptors to aid invasion. Many of these adhesins are subject to cleavage by rhomboid proteases (ROMs) within their transmembrane segments during invasion. Previous studies have demonstrated the importance of adhesin cleavage for parasite invasion and proposed that the ROMs responsible for processing would be essential for parasite survival. In T. gondii, ROM5 was thought to be the critical ROM for adhesin shedding due to its robust protease activity in vitro and posterior localization on the parasite surface. Here, we knocked out all three ROMs in T. gondii tachyzoites and found that ROM4, but not ROM5, was key for adhesin cleavage. However, none of the ROMs individually or in combination was essential for cell entry, further emphasizing that essential pathways such as invasion typically rely on redundant pathways to ensure survival.

scholarly journals Microevolution in the major outer membrane protein OmpA of Acinetobacter baumannii

2019 ◽  
Author(s):  
Alejandro M. Viale ◽  
Benjamin A. Evans
Keyword(s):  
Acinetobacter Baumannii ◽  
Host Cell ◽  
Outer Membrane ◽  
Biofilm Formation ◽  
Vaccine Design ◽  
Acinetobacter Calcoaceticus ◽  
Relevant Information ◽  
Cell Recognition ◽  
The Many ◽  
Host Cell Recognition

AbstractAcinetobacter baumannii is nowadays a relevant nosocomial pathogen characterized by multidrug resistance (MDR) and concomitant difficulties to treat infections. OmpA is the most abundant A. baumannii outer membrane (OM) protein, and is involved in virulence, host cell recognition, biofilm formation, regulation of OM stability, permeability, and antibiotic resistance. OmpA members are two-domain proteins with an N-terminal eight-stranded β-barrel domain with four external loops (ELs) interacting with the environment, and a C-terminal periplasmic domain binding non-covalently to the peptidoglycan. Here, we combined data from genome sequencing, phylogenetic, and multilocus sequence analyses from 242 strains of the Acinetobacter calcoaceticus/Acinetobacter baumannii complex (ACB), 222 from A. baumannii, to explore ompA microevolutionary divergence. Five major ompA variant groups were identified (V1 to V5) comprising 50 different alleles coding for 29 different proteins. Polymorphisms were concentrated in 5 regions corresponding to the four ELs and the C-terminal end, and provided evidence for different intra-genic recombination events. ompA variants were not randomly distributed across the A. baumannii phylogeny, with the most frequent V1a1 allele almost exclusive to clonal complex 1 (CC1) strains and the second most frequent V2a1 allele found in the majority of CC2 strains. Evidence was found for assortative exchanges of ompA alleles not only between different A. baumannii clonal lineages, but also different ACB species. Within A. baumannii ompA non-synonymous substitutions were concentrated in the ELs regions, but were more abundant in the transmembrane regions between different Acinetobacter species. The overall results have implications for A. baumannii evolution, epidemiology, virulence, and vaccine design.ImportanceAcinetobacter baumannii is an increasing MDR threat in nosocomial settings associated with prolonged hospitalization and concomitantly increased healthcare costs. The main A. baumannii OM protein, OmpA, is a multifaceted two-domain protein implicated in host cell recognition and adhesion, cytotoxicity, biofilm formation, and as a slow porin for antibiotics and small hydrophilic nutrients. A. baumannii OmpA has been proposed as a potential target for anti-virulence drugs and as a vaccine candidate. Given the many interactions of this protein with environmental factors including host defenses, it is certainly subjected to many selective pressures. Here, we analyzed the microevolution of this OM protein in the A. baumannii population to obtain clues on the extent to which selection in the clinical setting has shaped this protein. The results provide relevant information on the main causes driving evolution of this protein, with potential implications in A. baumannii epidemiology, virulence, and vaccine design.

scholarly journals Toxoplasma gondii Development of Its Replicative Niche: in Its Host Cell and Beyond

2014 ◽  
Vol 13 (8) ◽  
pp. 965-976 ◽  
Author(s):  
Ira J. Blader ◽  
Anita A. Koshy
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Host Cells ◽  
Content Type ◽  
Obligate Intracellular ◽  
Cellular Processes ◽  
High Prevalence ◽  
Life Threatening ◽  
Cell Processes ◽  
Cellular Pathways

ABSTRACTIntracellular pathogens can replicate efficiently only after they manipulate and modify their host cells to create an environment conducive to replication. While diverse cellular pathways are targeted by different pathogens, metabolism, membrane and cytoskeletal architecture formation, and cell death are the three primary cellular processes that are modified by infections.Toxoplasma gondiiis an obligate intracellular protozoan that infects ∼30% of the world's population and causes severe and life-threatening disease in developing fetuses, in immune-comprised patients, and in certain otherwise healthy individuals who are primarily found in South America. The high prevalence ofToxoplasmain humans is in large part a result of its ability to modulate these three host cell processes. Here, we highlight recent work defining the mechanisms by whichToxoplasmainteracts with these processes. In addition, we hypothesize why some processes are modified not only in the infected host cell but also in neighboring uninfected cells.

scholarly journals The Protozoan Parasite Toxoplasma gondii Selectively Reprograms the Host Cell Translatome

2018 ◽  
Vol 86 (9) ◽  
Author(s):  
Louis-Philippe Leroux ◽  
Julie Lorent ◽  
Tyson E. Graber ◽  
Visnu Chaparro ◽  
Laia Masvidal ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Cell Activation ◽  
Immune Cell ◽  
Mrna Translation ◽  
Protozoan Parasite ◽  
Translational Efficiency ◽  
Type I ◽  
Content Type ◽  
Infection Inhibition

ABSTRACT The intracellular parasite Toxoplasma gondii promotes infection by targeting multiple host cell processes; however, whether it modulates mRNA translation is currently unknown. Here, we show that infection of primary murine macrophages with type I or II T. gondii strains causes a profound perturbation of the host cell translatome. Notably, translation of transcripts encoding proteins involved in metabolic activity and components of the translation machinery was activated upon infection. In contrast, the translational efficiency of mRNAs related to immune cell activation and cytoskeleton/cytoplasm organization was largely suppressed. Mechanistically, T. gondii bolstered mechanistic target of rapamycin (mTOR) signaling to selectively activate the translation of mTOR-sensitive mRNAs, including those with a 5′-terminal oligopyrimidine (5′ TOP) motif and those encoding mitochondrion-related proteins. Consistent with parasite modulation of host mTOR-sensitive translation to promote infection, inhibition of mTOR activity suppressed T. gondii replication. Thus, selective reprogramming of host mRNA translation represents an important subversion strategy during T. gondii infection.

scholarly journals A Focused Small-Molecule Screen Identifies 14 Compounds with Distinct Effects on Toxoplasma gondii

2012 ◽  
Vol 56 (11) ◽  
pp. 5581-5590 ◽  
Author(s):  
Edwin T. Kamau ◽  
Ananth R. Srinivasan ◽  
Mark J. Brown ◽  
Matthew G. Fair ◽  
Erin J. Caraher ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Kinase Inhibitors ◽  
Severe Disease ◽  
Content Type ◽  
Cellular Target ◽  
Small Molecule Screen ◽  
Parasite Motility ◽  
Future Work

ABSTRACTToxoplasma gondiiis a globally ubiquitous pathogen that can cause severe disease in immunocompromised humans and the developing fetus. Given the proven role ofToxoplasma-secreted kinases in the interaction ofToxoplasmawith its host cell, identification of novel kinase inhibitors could precipitate the development of new anti-Toxoplasmadrugs and define new pathways important for parasite survival. We selected a small (n= 527) but diverse set of putative kinase inhibitors and screened them for effects on the growth ofToxoplasmain vitro. We identified and validated 14 noncytotoxic compounds, all of which had 50% effective concentrations in the nanomolar to micromolar range. We further characterized eight of these compounds, four inhibitors and four enhancers, by determining their effects on parasite motility, invasion, and the likely cellular target (parasite or host cell). Only two compounds had an effect on parasite motility and invasion. All the inhibitors appeared to target the parasite, and interestingly, two of the enhancers appeared to rather target the host cell, suggesting modulation of host cell pathways beneficial for parasite growth. For the four inhibitors, we also tested their efficacy in a mouse model, where one compound proved potent. Overall, these 14 compounds represent a new and diverse set of small molecules that are likely targeting distinct parasite and host cell pathways. Future work will aim to characterize their molecular targets in both the host and parasite.

Sign in / Sign up

Export Citation Format

Share Document