Host Cell Invasion by Apicomplexan Parasites: Insights from the Co-Structure of AMA1 with a RON2 Peptide

The capacity to migrate is fundamental to multicellular and single-celled life. Apicomplexan parasites, an ancient protozoan clade that includes malaria parasites (Plasmodium) and Toxoplasma, achieve remarkable speeds of directional cell movement. This rapidity is achieved via a divergent actomyosin motor system, housed within a narrow compartment that lies underneath the length of the parasite plasma membrane. How this motor functions at a mechanistic level during motility and host cell invasion is a matter of debate. Here, we integrate old and new insights toward refining the current model for the function of this motor with the aim of revitalizing interest in the mechanics of how these deadly pathogens move.

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Not a Simple Tether: Binding of Toxoplasma gondii AMA1 to RON2 during Invasion Protects AMA1 from Rhomboid-Mediated Cleavage and Leads to Dephosphorylation of Its Cytosolic Tail

mBio ◽

10.1128/mbio.00754-16 ◽

2016 ◽

Vol 7 (5) ◽

Cited By ~ 13

Author(s):

Shruthi Krishnamurthy ◽

Bin Deng ◽

Roxana del Rio ◽

Kerry R. Buchholz ◽

Moritz Treeck ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Host Cell ◽

Cell Invasion ◽

Transmembrane Domain ◽

Critical Role ◽

Host Cells ◽

Receptor Protein ◽

Host Cell Invasion ◽

Cell Binding ◽

Apicomplexan Parasites

ABSTRACT Apical membrane antigen 1 (AMA1) is a receptor protein on the surface of Toxoplasma gondii that plays a critical role in host cell invasion. The ligand to which T . gondii AMA1 (TgAMA1) binds, TgRON2, is secreted into the host cell membrane by the parasite during the early stages of invasion. The TgAMA1-TgRON2 complex forms the core of the “moving junction,” a ring-shaped zone of tight contact between the parasite and host cell membranes, through which the parasite pushes itself during invasion. Paradoxically, the parasite also expresses rhomboid proteases that constitutively cleave the TgAMA1 transmembrane domain. How can TgAMA1 function effectively in host cell binding if its extracellular domain is constantly shed from the parasite surface? We show here that when TgAMA1 binds the domain 3 (D3) peptide of TgRON2, its susceptibility to cleavage by rhomboid protease(s) is greatly reduced. This likely serves to maintain parasite-host cell binding at the moving junction, a hypothesis supported by data showing that parasites expressing a hypercleavable version of TgAMA1 invade less efficiently than wild-type parasites do. Treatment of parasites with the D3 peptide was also found to reduce phosphorylation of S527 on the cytoplasmic tail of TgAMA1, and parasites expressing a phosphomimetic S527D allele of TgAMA1 showed an invasion defect. Taken together, these data suggest that TgAMA1-TgRON2 interaction at the moving junction protects TgAMA1 molecules that are actively engaged in host cell penetration from rhomboid-mediated cleavage and generates an outside-in signal that leads to dephosphorylation of the TgAMA1 cytosolic tail. Both of these effects are required for maximally efficient host cell invasion. IMPORTANCE Nearly one-third of the world’s population is infected with the protozoan parasite Toxoplasma gondii , which causes life-threatening disease in neonates and immunocompromised individuals. T. gondii is a member of the phylum Apicomplexa, which includes many other parasites of veterinary and medical importance, such as those that cause coccidiosis, babesiosis, and malaria. Apicomplexan parasites grow within their hosts through repeated cycles of host cell invasion, parasite replication, and host cell lysis. Parasites that cannot invade host cells cannot survive or cause disease. AMA1 is a highly conserved protein on the surface of apicomplexan parasites that is known to be important for invasion, and the work presented here reveals new and unexpected insights into AMA1 function. A more complete understanding of the role of AMA1 in invasion may ultimately contribute to the development of new chemotherapeutics designed to disrupt AMA1 function and invasion-related signaling in this important group of human pathogens.

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The moving junction, a key portal to host cell invasion by apicomplexan parasites

Current Opinion in Microbiology ◽

10.1016/j.mib.2012.02.007 ◽

2012 ◽

Vol 15 (4) ◽

pp. 449-455 ◽

Cited By ~ 37

Author(s):

Bang Shen ◽

L David Sibley

Keyword(s):

Host Cell ◽

Cell Invasion ◽

Host Cell Invasion ◽

Apicomplexan Parasites

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Conditional Expression of Toxoplasma gondii Apical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Molecular Biology of the Cell ◽

10.1091/mbc.e05-04-0281 ◽

2005 ◽

Vol 16 (9) ◽

pp. 4341-4349 ◽

Cited By ~ 179

Author(s):

Jeffrey Mital ◽

Markus Meissner ◽

Dominique Soldati ◽

Gary E. Ward

Keyword(s):

Toxoplasma Gondii ◽

Host Cell ◽

Cell Invasion ◽

Apical Membrane ◽

Conditional Knockout ◽

Host Cell Invasion ◽

Apical Membrane Antigen 1 ◽

Apicomplexan Parasites ◽

Apical Membrane Antigen ◽

Conditional Expression

Toxoplasma gondii is an obligate intracellular parasite and an important human pathogen. Relatively little is known about the proteins that orchestrate host cell invasion by T. gondii or related apicomplexan parasites (including Plasmodium spp., which cause malaria), due to the difficulty of studying essential genes in these organisms. We have used a recently developed regulatable promoter to create a conditional knockout of T. gondii apical membrane antigen-1 (TgAMA1). TgAMA1 is a transmembrane protein that localizes to the parasite's micronemes, secretory organelles that discharge during invasion. AMA1 proteins are conserved among apicomplexan parasites and are of intense interest as malaria vaccine candidates. We show here that T. gondii tachyzoites depleted of TgAMA1 are severely compromised in their ability to invade host cells, providing direct genetic evidence that AMA1 functions during invasion. The TgAMA1 deficiency has no effect on microneme secretion or initial attachment of the parasite to the host cell, but it does inhibit secretion of the rhoptries, organelles whose discharge is coupled to active host cell penetration. The data suggest a model in which attachment of the parasite to the host cell occurs in two distinct stages, the second of which requires TgAMA1 and is involved in regulating rhoptry secretion.

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Unconventional Specimen Preparation Techniques Using High Resolution Low Voltage Field Emission Scanning Electron Microscopy to Study Cell Motility, Host Cell Invasion, and Internal Cell Structures in Toxoplasma gondii

Microscopy and Microanalysis ◽

10.1017/s1431927601020025 ◽

2002 ◽

Vol 8 (2) ◽

pp. 94-103 ◽

Cited By ~ 9

Author(s):

Heide Schatten ◽

Hans Ris

Keyword(s):

Electron Microscopy ◽

Cell Division ◽

Host Cell ◽

Cell Invasion ◽

Low Voltage ◽

Cytoskeletal Proteins ◽

Specimen Preparation ◽

Host Cell Invasion ◽

Apicomplexan Parasites ◽

Preparation Techniques

Apicomplexan parasites employ complex and unconventional mechanisms for cell locomotion, host cell invasion, and cell division that are only poorly understood. While immunofluorescence and conventional transmission electron microscopy have been used to answer questions about the localization of some cytoskeletal proteins and cell organelles, many questions remain unanswered, partly because new methods are needed to study the complex interactions of cytoskeletal proteins and organelles that play a role in cell locomotion, host cell invasion, and cell division. The choice of fixation and preparation methods has proven critical for the analysis of cytoskeletal proteins because of the rapid turnover of actin filaments and the dense spatial organization of the cytoskeleton and its association with the complex membrane system. Here we introduce new methods to study structural aspects of cytoskeletal motility, host cell invasion, and cell division of Toxoplasma gondii, a most suitable laboratory model that is representative of apicomplexan parasites. The novel approach in our experiments is the use of high resolution low voltage field emission scanning electron microscopy (LVFESEM) combined with two new specimen preparation techniques. The first method uses LVFESEM after membrane extraction and stabilization of the cytoskeleton. This method allows viewing of actin filaments which had not been possible with any other method available so far. The second approach of imaging the parasite's ultrastructure and interactions with host cells uses semithick sections (200 nm) that are resin de-embedded (Ris and Malecki, 1993) and imaged with LVFESEM. This method allows analysis of structural detail in the parasite before and after host cell invasion and interactions with the membrane of the parasitophorous vacuole as well as parasite cell division.

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Host Cell Invasion by Apicomplexan Parasites: The Junction Conundrum

PLoS Pathogens ◽

10.1371/journal.ppat.1004273 ◽

2014 ◽

Vol 10 (9) ◽

pp. e1004273 ◽

Cited By ~ 52

Author(s):

Daniel Bargieri ◽

Vanessa Lagal ◽

Nicole Andenmatten ◽

Isabelle Tardieux ◽

Markus Meissner ◽

...

Keyword(s):

Host Cell ◽

Cell Invasion ◽

Host Cell Invasion ◽

Apicomplexan Parasites

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High Resolution Low Voltage Field Emission Scanning Electron Microscopy on De-Embedded Thick Sections Reveals Structural Interactions of the Surface of the Apicomplexan Parasite Toxoplasma Gondii with the Host Cell in the Parasitophorous Vacuole

Microscopy and Microanalysis ◽

10.1017/s143192760003573x ◽

2000 ◽

Vol 6 (S2) ◽

pp. 648-649

Author(s):

Heide Schatten ◽

David Sibley ◽

Hans Ris

Keyword(s):

Toxoplasma Gondii ◽

Host Cell ◽

Cell Invasion ◽

Biochemical Characterization ◽

Low Voltage ◽

Cytoskeletal Proteins ◽

Host Cells ◽

Farm Animals ◽

Host Cell Invasion ◽

Apicomplexan Parasites

The protozoan parasite Toxoplasma gondii represents a large group of Apicomplexan parasites with a highly unusual motility system that is crucial for cell locomotion and host cell invasion. Studying the motility system and interactions with host cells will increase our knowledge on how to prevent infection. Apicomplexan parasites can cause considerable health problems to animals including sheep, goats, pigs, and chicken. Eimeria is known as a pathogen of coccidiosis in chicken, and Cryptosporidium causes cryptospiridiosis in cattle and other farm animals. Toxoplasma gondii can cause infection that results in abortion, central nervous disorders and death of stressed and immunocompromised farm animals. Common to all Apicomplexan parasites is an unconventional motility system that is thought to be actively involved in host-cell invasion. However, the structural and biochemical characterization of Apicomplexan parasites has proven more difficult than previously thought because of genetic and behavioral differences of the parasites’ cytoskeletal proteins that differ from those in well studied mammalian systems.

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Functional Analysis of Rhomboid Proteases during Toxoplasma Invasion

mBio ◽

10.1128/mbio.01795-14 ◽

2014 ◽

Vol 5 (5) ◽

Cited By ~ 39

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.

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Structural insights into an atypical secretory pathway kinase crucial for Toxoplasma gondii invasion

Nature Communications ◽

10.1038/s41467-021-24083-y ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Gaëlle Lentini ◽

Rouaa Ben Chaabene ◽

Oscar Vadas ◽

Chandra Ramakrishnan ◽

Budhaditya Mukherjee ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Host Cell ◽

Cell Invasion ◽

Plasma Membranes ◽

Secretory Pathway ◽

Host Cell Invasion ◽

Host Cell Membrane ◽

Apicomplexan Parasites ◽

Cell Plasma ◽

Structural Insights

AbstractActive host cell invasion by the obligate intracellular apicomplexan parasites relies on the formation of a moving junction, which connects parasite and host cell plasma membranes during entry. Invading Toxoplasma gondii tachyzoites secrete their rhoptry content and insert a complex of RON proteins on the cytoplasmic side of the host cell membrane providing an anchor to which the parasite tethers. Here we show that a rhoptry-resident kinase RON13 is a key virulence factor that plays a crucial role in host cell entry. Cryo-EM, kinase assays, phosphoproteomics and cellular analyses reveal that RON13 is a secretory pathway kinase of atypical structure that phosphorylates rhoptry proteins including the components of the RON complex. Ultimately, RON13 kinase activity controls host cell invasion by anchoring the moving junction at the parasite-host cell interface.

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