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Mukherjee S, Nasamu AS, Rubiano KC, Goldberg DE. Activation of the Plasmodium Egress Effector Subtilisin-Like Protease 1 Is Mediated by Plasmepsin X Destruction of the Prodomain. mBio 2023; 14:e0067323. [PMID: 37036362 PMCID: PMC10128010 DOI: 10.1128/mbio.00673-23] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 03/20/2023] [Indexed: 04/11/2023] Open
Abstract
Following each round of replication, daughter merozoites of the malaria parasite Plasmodium falciparum escape (egress) from the infected host red blood cell (RBC) by rupturing the parasitophorous vacuole membrane (PVM) and the RBC membrane (RBCM). A proteolytic cascade orchestrated by a parasite serine protease, subtilisin-like protease 1 (SUB1), regulates the membrane breakdown. SUB1 activation involves primary autoprocessing of the 82-kDa zymogen to a 54-kDa (p54) intermediate that remains bound to its inhibitory propiece (p31) postcleavage. A second processing step converts p54 to the terminal 47-kDa (p47) form of SUB1. Although the aspartic protease plasmepsin X (PM X) has been implicated in the activation of SUB1, the mechanism remains unknown. Here, we show that upon knockdown of PM X, the inhibitory p31-p54 complex of SUB1 accumulates in the parasites. Using recombinant PM X and SUB1, we show that PM X can directly cleave both p31 and p54. We have mapped the cleavage sites on recombinant p31. Furthermore, we demonstrate that the conversion of p54 to p47 can be effected by cleavage at either SUB1 or PM X cleavage sites that are adjacent to one another. Importantly, once the p31 is removed, p54 is fully functional inside the parasites, suggesting that the conversion to p47 is dispensable for SUB1 activity. Relief of propiece inhibition via a heterologous protease is a novel mechanism for subtilisin activation. IMPORTANCE Malaria parasites replicate inside a parasitophorous vacuole within the host red blood cells. The exit of mature progeny from the infected host cells is essential for further dissemination. Parasite exit is a highly regulated, explosive process that involves membrane breakdown. To do this, the parasite utilizes a serine protease called SUB1 that proteolytically activates various effector proteins. SUB1 activity is dependent on an upstream protease called PM X, although the mechanism was unknown. Here, we describe the molecular basis for PM X-mediated SUB1 activation. PM X proteolytically degrades the inhibitory segment of SUB1, thereby activating it. The involvement of a heterologous protease is a novel mechanism for subtilisin activation.
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Affiliation(s)
- Sumit Mukherjee
- Division of Infectious Diseases, Department of Medicine, and Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Armiyaw S. Nasamu
- Division of Infectious Diseases, Department of Medicine, and Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Kelly C. Rubiano
- Division of Infectious Diseases, Department of Medicine, and Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Daniel E. Goldberg
- Division of Infectious Diseases, Department of Medicine, and Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA
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Mukherjee S, Nasamu AS, Rubiano K, Goldberg DE. Activation of the Plasmodium egress effector subtilisin-like protease 1 is achieved by plasmepsin X destruction of the propiece. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.13.524002. [PMID: 36712005 PMCID: PMC9882241 DOI: 10.1101/2023.01.13.524002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Following each round of replication, daughter merozoites of the malaria parasite Plasmodium falciparum escape (egress) from the infected host red blood cell (RBC) by rupturing the parasitophorous vacuole membrane (PVM) and the RBC membrane (RBCM). A proteolytic cascade orchestrated by the parasite’s serine protease, subtilisin-like protease 1 (SUB1) regulates the membrane breakdown. SUB1 activation involves primary auto-processing of the 82 kDa zymogen to a 54 kDa (p54) intermediate that remains bound to its inhibitory propiece (p31) post cleavage. A second processing step converts p54 to the terminal 47 kDa (p47) form of SUB1. Although the aspartic protease plasmepsin X (PM X) has been implicated in the activation of SUB1, the mechanism remains unknown. Here, we show that upon knockdown of PM X the inhibitory p31/p54 complex of SUB1 accumulates in the parasites. Using recombinant PM X and SUB1, we show that PM X can directly cleave both p31 and p54. We have mapped the cleavage sites on recombinant p31. Furthermore, we demonstrate that the conversion of p54 to p47 can be effected by cleavage at either a SUB1 or PM X cleavage site that are adjacent to one another. Importantly once the p31 is removed, p54 is fully functional inside the parasites suggesting that the conversion to p47 is dispensable for SUB1 activity. Relief of propiece inhibition via a heterologous protease is a novel mechanism for subtilisin activation. Significance Statement Malaria parasites replicate inside a parasitophorous vacuole within the host red blood cells. Exit of mature progeny from the infected host cells is essential for further dissemination. Parasite exit is a highly regulated, explosive process that involves membrane breakdown. To do this, the parasite utilizes a serine protease, called the subtilisin-like protease 1 or SUB1 that proteolytically activates various effector proteins. SUB1 activity is dependent on an upstream protease, called plasmepsin X (PM X), although the mechanism was unknown. Here we describe the molecular basis for PM X mediated SUB1 activation. PM X proteolytically degrades the inhibitory segment of SUB1, thereby activating it. Involvement of a heterologous protease is a novel mechanism for subtilisin activation.
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Müller J, Anghel N, Imhof D, Hänggeli K, Uldry AC, Braga-Lagache S, Heller M, Ojo KK, Ortega-Mora LM, Van Voorhis WC, Hemphill A. Common Molecular Targets of a Quinolone Based Bumped Kinase Inhibitor in Neospora caninum and Danio rerio. Int J Mol Sci 2022; 23:2381. [PMID: 35216497 PMCID: PMC8879773 DOI: 10.3390/ijms23042381] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Revised: 02/16/2022] [Accepted: 02/17/2022] [Indexed: 12/30/2022] Open
Abstract
Neospora caninum is an apicomplexan parasite closely related to Toxoplasma gondii, and causes abortions, stillbirths and/or fetal malformations in livestock. Target-based drug development has led to the synthesis of calcium-dependent protein kinase 1 inhibitors, collectively named bumped kinase inhibitors (BKIs). Previous studies have shown that several BKIs have excellent efficacy against neosporosis in vitro and in vivo. However, several members of this class of compounds impair fertility in pregnant mouse models and cause embryonic malformation in a zebrafish (Danio rerio) model. Similar to the first-generation antiprotozoal drug quinine, some BKIs have a quinoline core structure. To identify common targets in both organisms, we performed differential affinity chromatography with cell-free extracts from N. caninum tachyzoites and D. rerio embryos using the 5-aminopyrazole-4-carboxamide (AC) compound BKI-1748 and quinine columns coupled to epoxy-activated sepharose followed by mass spectrometry. BKI-binding proteins of interest were identified in eluates from columns coupled to BKI-1748, or in eluates from BKI-1748 as well as quinine columns. In N. caninum, 12 proteins were bound specifically to BKI-1748 alone, and 105 proteins, including NcCDPK1, were bound to both BKI-1748 and quinine. For D. rerio, the corresponding numbers were 13 and 98 binding proteins, respectively. In both organisms, a majority of BKI-1748 binding proteins was involved in RNA binding and modification, in particular, splicing. Moreover, both datasets contained proteins involved in DNA binding or modification and key steps of intermediate metabolism. These results suggest that BKI-1748 interacts with not only specific targets in apicomplexans, such as CDPK1, but also with targets in other eukaryotes, which are involved in common, essential pathways.
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Affiliation(s)
- Joachim Müller
- Institute of Parasitology, Vetsuisse Faculty, University of Bern, Länggass-Strasse 122, 3012 Bern, Switzerland; (J.M.); (N.A.); (D.I.); (K.H.)
| | - Nicoleta Anghel
- Institute of Parasitology, Vetsuisse Faculty, University of Bern, Länggass-Strasse 122, 3012 Bern, Switzerland; (J.M.); (N.A.); (D.I.); (K.H.)
| | - Dennis Imhof
- Institute of Parasitology, Vetsuisse Faculty, University of Bern, Länggass-Strasse 122, 3012 Bern, Switzerland; (J.M.); (N.A.); (D.I.); (K.H.)
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Mittelstrasse 43, 3012 Bern, Switzerland
| | - Kai Hänggeli
- Institute of Parasitology, Vetsuisse Faculty, University of Bern, Länggass-Strasse 122, 3012 Bern, Switzerland; (J.M.); (N.A.); (D.I.); (K.H.)
- Graduate School for Cellular and Biomedical Sciences, University of Bern, Mittelstrasse 43, 3012 Bern, Switzerland
| | - Anne-Christine Uldry
- Proteomics and Mass Spectrometry Core Facility, Department for BioMedical Research (DBMR), University of Bern, 3008 Bern, Switzerland; (A.-C.U.); (S.B.-L.); (M.H.)
| | - Sophie Braga-Lagache
- Proteomics and Mass Spectrometry Core Facility, Department for BioMedical Research (DBMR), University of Bern, 3008 Bern, Switzerland; (A.-C.U.); (S.B.-L.); (M.H.)
| | - Manfred Heller
- Proteomics and Mass Spectrometry Core Facility, Department for BioMedical Research (DBMR), University of Bern, 3008 Bern, Switzerland; (A.-C.U.); (S.B.-L.); (M.H.)
| | - Kayode K. Ojo
- Center for Emerging and Re-Emerging Infectious Diseases (CERID), Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA 98109, USA; (K.K.O.); (W.C.V.V.)
| | - Luis-Miguel Ortega-Mora
- SALUVET, Animal Health Department, Faculty of Veterinary Sciences, Complutense University of Madrid, 28040 Madrid, Spain;
| | - Wesley C. Van Voorhis
- Center for Emerging and Re-Emerging Infectious Diseases (CERID), Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA 98109, USA; (K.K.O.); (W.C.V.V.)
| | - Andrew Hemphill
- Institute of Parasitology, Vetsuisse Faculty, University of Bern, Länggass-Strasse 122, 3012 Bern, Switzerland; (J.M.); (N.A.); (D.I.); (K.H.)
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Zhu YC, Ma LJ, Zhang JL, Liu JF, He Y, Feng JY, Chen J. Protective Immunity Induced by TgMIC5 and TgMIC16 DNA Vaccines Against Toxoplasmosis. Front Cell Infect Microbiol 2021; 11:686004. [PMID: 34595126 PMCID: PMC8476850 DOI: 10.3389/fcimb.2021.686004] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Accepted: 08/23/2021] [Indexed: 11/13/2022] Open
Abstract
Toxoplasma gondii is an obligate intracellular parasite, which is responsible for a widely distributed zoonosis. Effective vaccines against toxoplasmosis are necessary to protect the public health. The aim of this study is to evaluate the immune efficacy of DNA vaccines encoding TgMIC5 and TgMIC16 genes against T. gondii infection. The recombinant plasmid pVAX-MIC5 and pVAX-MIC16 were constructed and injected intramuscularly in mice. The specific immune responses and protection against challenge with T. gondii RH tachyzoites were evaluated by measuring the cytokine levels, serum antibody concentrations, lymphocyte proliferation, lymphocyte populations, and the survival time. The protection against challenge with the T. gondii RH tchyzoites and PRU cysts was examined by evaluation of the reduction in the brain cyst burden. The results indicated that immunized mice showed significantly increased levels of IgG, IFN-γ, IL-2, IL-12p70, and IL-12p40 and percentages of CD4+ and CD8+ T cells. Additionally, vaccination prolonged the mouse survival time and reduced brain cysts compared with controls. Mouse groups immunized with a two-gene cocktail of pVAX-MIC5 + pVAX-MIC16 were more protected than mouse groups immunized with a single gene of pVAX-MIC5 or pVAX-MIC16. These results demonstrate that TgMIC5 and TgMIC16 induce effective immunity against toxoplasmosis and may serve as a good vaccine candidate against T. gondii infection.
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Affiliation(s)
- Yu-Chao Zhu
- Department of Radiology, The Affiliated Hospital of Medical School of Ningbo University, Ningbo University School of Medicine, Ningbo, China
| | - Li-Juan Ma
- Department of Integrated Chinese and Western Medicine Oncology, The Affiliated People's Hospital of Ningbo University, Ningbo, China
| | - Ji-Li Zhang
- Department of Radiology, The Affiliated Hospital of Medical School of Ningbo University, Ningbo University School of Medicine, Ningbo, China
| | - Jian-Fa Liu
- Immunology Innovation Team, Ningbo University School of Medicine, Ningbo, China
| | - Yong He
- Department of Radiology, The Affiliated Hospital of Medical School of Ningbo University, Ningbo University School of Medicine, Ningbo, China
| | - Ji-Ye Feng
- Department of Hepatobiliary Surgery, The Affiliated People's Hospital of Ningbo University, Ningbo, China
| | - Jia Chen
- Department of Radiology, The Affiliated Hospital of Medical School of Ningbo University, Ningbo University School of Medicine, Ningbo, China.,Immunology Innovation Team, Ningbo University School of Medicine, Ningbo, China
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Marugan-Hernandez V, Sanchez-Arsuaga G, Vaughan S, Burrell A, Tomley FM. Do All Coccidia Follow the Same Trafficking Rules? Life (Basel) 2021; 11:life11090909. [PMID: 34575057 PMCID: PMC8465013 DOI: 10.3390/life11090909] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 08/24/2021] [Accepted: 08/27/2021] [Indexed: 01/06/2023] Open
Abstract
The Coccidia are a subclass of the Apicomplexa and include several genera of protozoan parasites that cause important diseases in humans and animals, with Toxoplasma gondii becoming the ‘model organism’ for research into the coccidian molecular and cellular processes. The amenability to the cultivation of T. gondii tachyzoites and the wide availability of molecular tools for this parasite have revealed many mechanisms related to their cellular trafficking and roles of parasite secretory organelles, which are critical in parasite-host interaction. Nevertheless, the extrapolation of the T. gondii mechanisms described in tachyzoites to other coccidian parasites should be done carefully. In this review, we considered published data from Eimeria parasites, a coccidian genus comprising thousands of species whose infections have important consequences in livestock and poultry. These studies suggest that the Coccidia possess both shared and diversified mechanisms of protein trafficking and secretion potentially linked to their lifecycles. Whereas trafficking and secretion appear to be well conversed prior to and during host-cell invasion, important differences emerge once endogenous development commences. Therefore, further studies to validate the mechanisms described in T. gondii tachyzoites should be performed across a broader range of coccidians (including T. gondii sporozoites). In addition, further genus-specific research regarding important disease-causing Coccidia is needed to unveil the individual molecular mechanisms of pathogenesis related to their specific lifecycles and hosts.
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Affiliation(s)
- Virginia Marugan-Hernandez
- The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms AL9 7TA, UK; (G.S.-A.); (F.M.T.)
- Correspondence: ; Tel.: +44-(0)-17-0766-9445
| | - Gonzalo Sanchez-Arsuaga
- The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms AL9 7TA, UK; (G.S.-A.); (F.M.T.)
| | - Sue Vaughan
- Department of Biological and Medical Sciences, Oxford Brookes University, Gipsy Lane, Oxford OX3 0BP, UK;
| | - Alana Burrell
- Electron Microscopy Science Technology Platform, The Francis Crick Institute, London NW1 1AT, UK;
| | - Fiona M. Tomley
- The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms AL9 7TA, UK; (G.S.-A.); (F.M.T.)
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Abstract
Apicomplexan protozoan parasites, such as those causing malaria and toxoplasmosis, must invade the cells of their hosts in order to establish a pathogenic infection. Timely release of proteins from a series of apical organelles is required for invasion. Neither the vesicular fusion events that underlie secretion nor the observed reliance of the various processes on changes in intracellular calcium concentrations is completely understood. We identified a group of three proteins with strong homology to the calcium-sensing ferlin family, which are known to be involved in protein secretion in other organisms. Surprisingly, decreasing the amounts of one of these proteins (TgFER2) did not have any effect on the typically calcium-dependent steps in invasion. Instead, TgFER2 was essential for the release of proteins from organelles called rhoptries. These data provide a tantalizing first look at the mechanisms controlling the very poorly understood process of rhoptry secretion, which is essential for the parasite’s infection cycle. Invasion of host cells by apicomplexan parasites such as Toxoplasma gondii is critical for their infectivity and pathogenesis. In Toxoplasma, secretion of essential egress, motility, and invasion-related proteins from microneme organelles is regulated by oscillations of intracellular Ca2+. Later stages of invasion are considered Ca2+ independent, including the secretion of proteins required for host cell entry and remodeling from the parasite’s rhoptries. We identified a family of three Toxoplasma proteins with homology to the ferlin family of double C2 domain-containing Ca2+ sensors. In humans and model organisms, such Ca2+ sensors orchestrate Ca2+-dependent exocytic membrane fusion with the plasma membrane. Here we focus on one ferlin that is conserved across the Apicomplexa, T. gondii FER2 (TgFER2). Unexpectedly, conditionally TgFER2-depleted parasites secreted their micronemes normally and were completely motile. However, these parasites were unable to invade host cells and were therefore not viable. Knockdown of TgFER2 prevented rhoptry secretion, and these parasites failed to form the moving junction at the parasite-host interface necessary for host cell invasion. Collectively, these data demonstrate the requirement of TgFER2 for rhoptry secretion in Toxoplasma tachyzoites and suggest a possible Ca2+ dependence of rhoptry secretion. These findings provide the first mechanistic insights into this critical yet poorly understood aspect of apicomplexan host cell invasion.
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Morlon-Guyot J, El Hajj H, Martin K, Fois A, Carrillo A, Berry L, Burchmore R, Meissner M, Lebrun M, Daher W. A proteomic analysis unravels novel CORVET and HOPS proteins involved in Toxoplasma gondii
secretory organelles biogenesis. Cell Microbiol 2018; 20:e12870. [DOI: 10.1111/cmi.12870] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 05/23/2018] [Accepted: 06/05/2018] [Indexed: 01/10/2023]
Affiliation(s)
- Juliette Morlon-Guyot
- Dynamique des Interactions Membranaires Normales et Pathologiques, UMR5235 CNRS, INSERM; Université de Montpellier; Montpellier France
| | - Hiba El Hajj
- Departments of Internal Medicine and Experimental Pathology, Immunology and Microbiology; American University of Beirut; Beirut Lebanon
| | - Kevin Martin
- Dynamique des Interactions Membranaires Normales et Pathologiques, UMR5235 CNRS, INSERM; Université de Montpellier; Montpellier France
| | - Adrien Fois
- Dynamique des Interactions Membranaires Normales et Pathologiques, UMR5235 CNRS, INSERM; Université de Montpellier; Montpellier France
| | - Amandine Carrillo
- Dynamique des Interactions Membranaires Normales et Pathologiques, UMR5235 CNRS, INSERM; Université de Montpellier; Montpellier France
| | - Laurence Berry
- Dynamique des Interactions Membranaires Normales et Pathologiques, UMR5235 CNRS, INSERM; Université de Montpellier; Montpellier France
| | | | - Markus Meissner
- Wellcome Centre for Molecular Parasitology; University of Glasgow; Glasgow UK
- Department of Veterinary Sciences, Experimental Parasitology; Ludwig-Maximilians-Universität München; Munich Germany
| | - Maryse Lebrun
- Dynamique des Interactions Membranaires Normales et Pathologiques, UMR5235 CNRS, INSERM; Université de Montpellier; Montpellier France
| | - Wassim Daher
- Dynamique des Interactions Membranaires Normales et Pathologiques, UMR5235 CNRS, INSERM; Université de Montpellier; Montpellier France
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Marugan-Hernandez V, Long E, Blake D, Crouch C, Tomley F. Eimeria tenella protein trafficking: differential regulation of secretion versus surface tethering during the life cycle. Sci Rep 2017; 7:4557. [PMID: 28676667 PMCID: PMC5496917 DOI: 10.1038/s41598-017-04049-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 05/08/2017] [Indexed: 01/15/2023] Open
Abstract
Eimeria spp. are intracellular parasites that have a major impact on poultry. Effective live vaccines are available and the development of reverse genetic technologies has raised the prospect of using Eimeria spp. as recombinant vectors to express additional immunoprotective antigens. To study the ability of Eimeria to secrete foreign antigens or display them on the surface of the sporozoite, transiently transfected populations of E. tenella expressing the fluorescent protein mCherry, linked to endogenous signal peptide (SP) and glycophosphatidylinositol-anchor (GPI) sequences, were examined. The SP from microneme protein EtMIC2 (SP2) allowed efficient trafficking of mCherry to cytoplasmic vesicles and following the C-terminal addition of a GPI-anchor (from surface antigen EtSAG1) mCherry was expressed on the sporozoite surface. In stable transgenic populations, mCherry fused to SP2 was secreted into the sporocyst cavity of the oocysts and after excystation, secretion was detected in culture supernatants but not into the parasitophorous vacuole after invasion. When the GPI was incorporated, mCherry was observed on the sporozites surface and in the supernatant of invading sporozoites. The proven secretion and surface exposure of mCherry suggests that antigen fusions with SP2 and GPI of EtSAG1 may be promising candidates to examine induction of protective immunity against heterologous pathogens.
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Affiliation(s)
- V Marugan-Hernandez
- The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms, AL9 7TA, UK.
| | - E Long
- The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms, AL9 7TA, UK
| | - D Blake
- The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms, AL9 7TA, UK
| | - C Crouch
- MSD Animal Health, Walton Manor, Milton Keynes, MK7 7AJ, UK
| | - F Tomley
- The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms, AL9 7TA, UK
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Rugarabamu G, Marq JB, Guérin A, Lebrun M, Soldati-Favre D. Distinct contribution of Toxoplasma gondii rhomboid proteases 4 and 5 to micronemal protein protease 1 activity during invasion. Mol Microbiol 2015; 97:244-62. [PMID: 25846828 DOI: 10.1111/mmi.13021] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/31/2015] [Indexed: 10/23/2022]
Abstract
Host cell entry by the Apicomplexa is associated with the sequential secretion of invasion factors from specialized apical organelles. Secretion of micronemal proteins (MICs) complexes by Toxoplasma gondii facilitates parasite gliding motility, host cell attachment and entry, as well as egress from infected cells. The shedding of MICs during these steps is mediated by micronemal protein proteases MPP1, MPP2 and MPP3. The constitutive activity of MPP1 leads to the cleavage of transmembrane MICs and is linked to the surface rhomboid protease 4 (ROM4) and possibly to rhomboid protease 5 (ROM5). To determine their importance and respective contribution to MPP1 activity, in this study ROM4 and ROM5 genes were abrogated using Cre-recombinase and CRISPR-Cas9 nuclease, respectively, and shown to be dispensable for parasite survival. Parasites lacking ROM4 predominantly engage in twirling motility and exhibit enhanced attachment and impaired invasion, whereas intracellular growth and egress is not affected. The substrates MIC2 and MIC6 are not cleaved in rom4-ko parasites, in contrast, intramembrane cleavage of AMA1 is reduced but not completely abolished. Shedding of MICs and invasion are not altered in the absence of ROM5; however, this protease responsible for the residual cleavage of AMA1 is able to cleave other AMA family members and exhibits a detectable contribution to invasion in the absence of ROM4.
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Affiliation(s)
- George Rugarabamu
- Department of Microbiology and Molecular Medicine, CMU, University of Geneva, 1 Rue Michel-Servet, 1211, Geneva 4, Switzerland
| | - Jean-Baptiste Marq
- Department of Microbiology and Molecular Medicine, CMU, University of Geneva, 1 Rue Michel-Servet, 1211, Geneva 4, Switzerland
| | - Amandine Guérin
- UMR 5235 CNRS, Université de Montpellier 2, 34095, Montpellier, France
| | - Maryse Lebrun
- UMR 5235 CNRS, Université de Montpellier 2, 34095, Montpellier, France
| | - Dominique Soldati-Favre
- Department of Microbiology and Molecular Medicine, CMU, University of Geneva, 1 Rue Michel-Servet, 1211, Geneva 4, Switzerland
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Microbial peptidyl-prolyl cis/trans isomerases (PPIases): virulence factors and potential alternative drug targets. Microbiol Mol Biol Rev 2015; 78:544-71. [PMID: 25184565 DOI: 10.1128/mmbr.00015-14] [Citation(s) in RCA: 121] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Initially discovered in the context of immunomodulation, peptidyl-prolyl cis/trans isomerases (PPIases) were soon identified as enzymes catalyzing the rate-limiting protein folding step at peptidyl bonds preceding proline residues. Intense searches revealed that PPIases are a superfamily of proteins consisting of three structurally distinguishable families with representatives in every described species of prokaryote and eukaryote and, recently, even in some giant viruses. Despite the clear-cut enzymatic activity and ubiquitous distribution of PPIases, reports on solely PPIase-dependent biological roles remain scarce. Nevertheless, they have been found to be involved in a plethora of biological processes, such as gene expression, signal transduction, protein secretion, development, and tissue regeneration, underscoring their general importance. Hence, it is not surprising that PPIases have also been identified as virulence-associated proteins. The extent of contribution to virulence is highly variable and dependent on the pleiotropic roles of a single PPIase in the respective pathogen. The main objective of this review is to discuss this variety in virulence-related bacterial and protozoan PPIases as well as the involvement of host PPIases in infectious processes. Moreover, a special focus is given to Legionella pneumophila macrophage infectivity potentiator (Mip) and Mip-like PPIases of other pathogens, as the best-characterized virulence-related representatives of this family. Finally, the potential of PPIases as alternative drug targets and first tangible results are highlighted.
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Zhang Z, Huang J, Li M, Sui Y, Wang S, Liu L, Xu L, Yan R, Song X, Li X. Identification and molecular characterization of microneme 5 of Eimeria acervulina. PLoS One 2014; 9:e115411. [PMID: 25531898 PMCID: PMC4274027 DOI: 10.1371/journal.pone.0115411] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 11/23/2014] [Indexed: 11/18/2022] Open
Abstract
In the present study, the microneme 5 gene of Eimeria acervulina (E. acervulina) (EaMIC5) was cloned and characterized. Specific primers for the rapid amplification of cDNA ends (RACE) were designed based on the expressed sequence tag (EST, GenBank Accession No. EH386430.1) to amplify the 3'- and 5'-ends of EaMIC5. The full length cDNA of this gene was obtained by overlapping the sequences of 3'- and 5'-extremities and amplification by reverse transcription PCR. Sequence analysis revealed that the open reading frame (ORF) of EaMIC5 was 336 bp and encoded a protein of 111 amino acids with 12.18 kDa. The ORF was inserted into pET-32a (+) to produce recombinant EaMIC5. Using western blotting assay, the recombinant protein was successfully recognized by the sera of chicks experimentally infected with E. acervulina, while the native protein in the somatic extract of sporozoites was as well detected by sera from rats immunized with the recombinant protein of EaMIC5. Immunofluorescence analysis using antibody against recombinant protein EaMIC5 indicated that this protein was expressed in the sporozoites and merozoites stages of E. acervulina. Animal challenge experiments demonstrated that the recombinant protein of EaMIC5 could significantly increase the average body weight gains, decrease the mean lesion scores and the oocyst outputs of the immunized chickens, and presented anti-coccidial index (ACI) more than 160. All the above results suggested that the EaMIC5 was a novel E. acervulina antigen and could be an effective candidate for the development of a new vaccine against this parasite.
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Affiliation(s)
- ZhenChao Zhang
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - JingWei Huang
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - MengHui Li
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - YuXia Sui
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - Shuai Wang
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - LianRui Liu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - LiXin Xu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - RuoFeng Yan
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - XiaoKai Song
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
| | - XiangRui Li
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, PR China
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12
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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. 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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13
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Pollo-Oliveira L, Post H, Acencio ML, Lemke N, van den Toorn H, Tragante V, Heck AJR, Altelaar AFM, Yatsuda AP. Unravelling the Neospora caninum secretome through the secreted fraction (ESA) and quantification of the discharged tachyzoite using high-resolution mass spectrometry-based proteomics. Parasit Vectors 2013; 6:335. [PMID: 24267406 PMCID: PMC4182915 DOI: 10.1186/1756-3305-6-335] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 11/15/2013] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The apicomplexan parasite Neospora caninum causes neosporosis, a disease that leads to abortion or stillbirth in cattle, generating an economic impact on the dairy and beef cattle trade. As an obligatory intracellular parasite, N. caninum needs to invade the host cell in an active manner to survive. The increase in parasite cytosolic Ca2+ upon contact with the host cell mediates critical events, including the exocytosis of phylum-specific secretory organelles and the activation of the parasite invasion motor. Because invasion is considered a requirement for pathogen survival and replication within the host, the identification of secreted proteins (secretome) involved in invasion may be useful to reveal interesting targets for therapeutic intervention. METHODS To chart the currently missing N. caninum secretome, we employed mass spectrometry-based proteomics to identify proteins present in the N. caninum tachyzoite using two different approaches. The first approach was identifying the proteins present in the tachyzoite-secreted fraction (ESA). The second approach was determining the relative quantification through peptide stable isotope labelling of the tachyzoites submitted to an ethanol secretion stimulus (discharged tachyzoite), expecting to identify the secreted proteins among the down-regulated group. RESULTS As a result, 615 proteins were identified at ESA and 2,011 proteins quantified at the discharged tachyzoite. We have analysed the connection between the secreted and the down-regulated proteins and searched for putative regulators of the secretion process among the up-regulated proteins. An interaction network was built by computational prediction involving the up- and down-regulated proteins. The mass spectrometry proteomics data have been deposited to the ProteomeXchange with identifier PXD000424. CONCLUSIONS The comparison between the protein abundances in ESA and their measure in the discharged tachyzoite allowed for a more precise identification of the most likely secreted proteins. Information from the network interaction and up-regulated proteins was important to recognise key proteins potentially involved in the metabolic regulation of secretion. Our results may be helpful to guide the selection of targets to be investigated against Neospora caninum and other Apicomplexan organisms.
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Affiliation(s)
- Letícia Pollo-Oliveira
- Faculdade de Ciências Farmacêuticas de Ribeirão Preto e Núcleo de Apoio à Pesquisa em Produtos Naturais e Sintéticos (NPPNS), Universidade de São Paulo, Av do Café , s/n, Ribeirão Preto, SP 14040-903, Brazil
| | - Harm Post
- Biomolecular Mass Spectrometry and Proteomics, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, Utrecht 3884 CH, The Netherlands
- Netherlands Proteomics Centre, Padualaan 8, Utrecht 3884 CH, The Netherlands
| | - Marcio Luis Acencio
- Botucatu Institute of Biosciences, UNESP - Univ Estadual Paulista, Distrito de Rubião Jr, s/n, Botucatu, São Paulo 18918-970, Brazil
| | - Ney Lemke
- Botucatu Institute of Biosciences, UNESP - Univ Estadual Paulista, Distrito de Rubião Jr, s/n, Botucatu, São Paulo 18918-970, Brazil
| | - Henk van den Toorn
- Biomolecular Mass Spectrometry and Proteomics, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, Utrecht 3884 CH, The Netherlands
- Netherlands Proteomics Centre, Padualaan 8, Utrecht 3884 CH, The Netherlands
| | - Vinicius Tragante
- Division of Heart and Lungs, Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands
- Division of Biomedical Genetics, Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Albert JR Heck
- Biomolecular Mass Spectrometry and Proteomics, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, Utrecht 3884 CH, The Netherlands
- Netherlands Proteomics Centre, Padualaan 8, Utrecht 3884 CH, The Netherlands
| | - AF Maarten Altelaar
- Biomolecular Mass Spectrometry and Proteomics, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, Utrecht 3884 CH, The Netherlands
- Netherlands Proteomics Centre, Padualaan 8, Utrecht 3884 CH, The Netherlands
| | - Ana Patrícia Yatsuda
- Faculdade de Ciências Farmacêuticas de Ribeirão Preto e Núcleo de Apoio à Pesquisa em Produtos Naturais e Sintéticos (NPPNS), Universidade de São Paulo, Av do Café , s/n, Ribeirão Preto, SP 14040-903, Brazil
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14
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McCoy JM, Whitehead L, van Dooren GG, Tonkin CJ. TgCDPK3 regulates calcium-dependent egress of Toxoplasma gondii from host cells. PLoS Pathog 2012; 8:e1003066. [PMID: 23226109 PMCID: PMC3514314 DOI: 10.1371/journal.ppat.1003066] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 10/15/2012] [Indexed: 12/11/2022] Open
Abstract
The phylum Apicomplexa comprises a group of obligate intracellular parasites of broad medical and agricultural significance, including Toxoplasma gondii and the malaria-causing Plasmodium spp. Key to their parasitic lifestyle is the need to egress from an infected cell, actively move through tissue, and reinvade another cell, thus perpetuating infection. Ca(2+)-mediated signaling events modulate key steps required for host cell egress, invasion and motility, including secretion of microneme organelles and activation of the force-generating actomyosin-based motor. Here we show that a plant-like Calcium-Dependent Protein Kinase (CDPK) in T. gondii, TgCDPK3, which localizes to the inner side of the plasma membrane, is not essential to the parasite but is required for optimal in vitro growth. We demonstrate that TgCDPK3, the orthologue of Plasmodium PfCDPK1, regulates Ca(2+) ionophore- and DTT-induced host cell egress, but not motility or invasion. Furthermore, we show that targeting to the inner side of the plasma membrane by dual acylation is required for its activity. Interestingly, TgCDPK3 regulates microneme secretion when parasites are intracellular but not extracellular. Indeed, the requirement for TgCDPK3 is most likely determined by the high K(+) concentration of the host cell. Our results therefore suggest that TgCDPK3's role differs from that previously hypothesized, and rather support a model where this kinase plays a role in rapidly responding to Ca(2+) signaling in specific ionic environments to upregulate multiple processes required for gliding motility.
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Affiliation(s)
- James M. McCoy
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
| | - Lachlan Whitehead
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
| | - Giel G. van Dooren
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Christopher J. Tonkin
- The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
- Department of Medical Biology, University of Melbourne, Melbourne, Australia
- * E-mail:
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15
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Saouros S, Dou Z, Henry M, Marchant J, Carruthers VB, Matthews S. Microneme protein 5 regulates the activity of Toxoplasma subtilisin 1 by mimicking a subtilisin prodomain. J Biol Chem 2012; 287:36029-40. [PMID: 22896704 DOI: 10.1074/jbc.m112.389825] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Toxoplasma gondii is the model parasite of the phylum Apicomplexa, which contains obligate intracellular parasites of medical and veterinary importance. Apicomplexans invade host cells by a multistep process involving the secretion of adhesive microneme protein (MIC) complexes. The subtilisin protease TgSUB1 trims several MICs on the parasite surface to activate gliding motility and host invasion. Although a previous study showed that expression of the secretory protein TgMIC5 suppresses TgSUB1 activity, the mechanism was unknown. Here, we solve the three-dimensional structure of TgMIC5 by nuclear magnetic resonance (NMR), revealing that it mimics a subtilisin prodomain including a flexible C-terminal peptide that may insert into the subtilisin active site. We show that TgMIC5 is an almost 50-fold more potent inhibitor of TgSUB1 activity than the small molecule inhibitor N-[N-(N-acetyl-L-leucyl)-L-leucyl]-L-norleucine (ALLN). Moreover, we demonstrate that TgMIC5 is retained on the parasite plasma membrane via its physical interaction with the membrane-anchored TgSUB1.
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Affiliation(s)
- Savvas Saouros
- Division of Molecular Biosciences, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
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16
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Gaji RY, Flammer HP, Carruthers VB. Forward targeting of Toxoplasma gondii proproteins to the micronemes involves conserved aliphatic amino acids. Traffic 2011; 12:840-53. [PMID: 21438967 DOI: 10.1111/j.1600-0854.2011.01192.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Like other apicomplexan parasites, Toxoplasma gondii actively invades host cells using a combination of secretory proteins and an acto-myosin motor system. Micronemes are the first set of proteins secreted during invasion that play an essential role in host cell entry. Many microneme proteins (MICs) function in protein complexes, and each complex contains at least one protein that displays a cleavable propeptide. Although MIC propeptides have been implicated in forward targeting to micronemes, the specific amino acids involved have not been identified. It was also not known if the propeptide has a general function in MICs trafficking in T. gondii and other apicomplexans. Here we show that propeptide domains are extensively interchangeable between T. gondii MICs and also with that of Eimeria tenella MIC5 (EtMIC5), suggesting a common mechanism of function. We also performed N-terminal deletion and mutational analysis of M2AP and MIC5 propeptides to show that a valine at position +3 (relative to signal peptidase cleavage) of proM2AP and a leucine at position +1 of proMIC5 are crucial for targeting to micronemes. Valine and leucine are closely related amino acids with similar side chains, implying a similar mode of function, a notion that was confirmed by correct trafficking of TgM2AP-V/L and TgMIC5-L/V substitution mutants. Propeptides of AMA1, MIC3 and EtMIC5 have valine or leucine at or near the N-termini and mutagenesis of these conserved residues validated their role in microneme trafficking. Collectively, our findings suggest that discrete, aliphatic residues at the extreme N-termini of proMICs facilitate trafficking to the micronemes.
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Affiliation(s)
- Rajshekhar Y Gaji
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
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17
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Lagal V, Binder EM, Huynh MH, Kafsack BFC, Harris PK, Diez R, Chen D, Cole RN, Carruthers VB, Kim K. Toxoplasma gondii protease TgSUB1 is required for cell surface processing of micronemal adhesive complexes and efficient adhesion of tachyzoites. Cell Microbiol 2011; 12:1792-808. [PMID: 20678172 DOI: 10.1111/j.1462-5822.2010.01509.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Host cell invasion by Toxoplasma gondii is critically dependent upon adhesive proteins secreted from the micronemes. Proteolytic trimming of microneme contents occurs rapidly after their secretion onto the parasite surface and is proposed to regulate adhesive complex activation to enhance binding to host cell receptors. However, the proteases responsible and their exact function are still unknown. In this report, we show that T. gondii tachyzoites lacking the microneme subtilisin protease TgSUB1 have a profound defect in surface processing of secreted microneme proteins. Notably parasites lack protease activity responsible for proteolytic trimming of MIC2, MIC4 and M2AP after release onto the parasite surface. Although complementation with full-length TgSUB1 restores processing, complementation of Δsub1 parasites with TgSUB1 lacking the GPI anchor (Δsub1::ΔGPISUB1) only partially restores microneme protein processing. Loss of TgSUB1 decreases cell attachment and in vitro gliding efficiency leading to lower initial rates of invasion. Δsub1 and Δsub1::ΔGPISUB1 parasites are also less virulent in mice. Thus TgSUB1 is involved in micronemal protein processing and regulation of adhesive properties of macromolecular adhesive complexes involved in host cell invasion.
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Affiliation(s)
- Vanessa Lagal
- Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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18
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A transient forward-targeting element for microneme-regulated secretion in Toxoplasma gondii. Biol Cell 2008; 100:253-64. [PMID: 17995454 DOI: 10.1042/bc20070076] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND INFORMATION Accurate sorting of proteins to the three types of secretory granules in Toxoplasma gondii is crucial for successful cell invasion by this obligate intracellular parasite. As in other eukaryotic systems, propeptide sequences are a common yet poorly understood feature of proteins destined for regulated secretion, which for Toxoplasma occurs through two distinct invasion organelles, rhoptries and micronemes. Microneme discharge during parasite apical attachment plays a pivotal role in cell invasion by delivering adhesive proteins for host receptor engagement. RESULTS We show here that the small micronemal proprotein MIC5 (microneme protein-5) undergoes proteolytic maturation at a site beyond the Golgi, and only the processed form of MIC5 is secreted via the micronemes. Proper cleavage of the MIC5 propeptide relies on an arginine residue in the P1' position, although P1' mutants are still cleaved to a lesser extent at an alternative site downstream of the primary site. Nonetheless, this aberrantly cleaved species still correctly traffics to the micronemes, indicating that correct cleavage is not necessary for micronemal targeting. In contrast, a deletion mutant lacking the propeptide was retained within the secretory system, principally in the ER (endoplasmic reticulum). The MIC5 propeptide also supported correct trafficking when exchanged for the M2AP propeptide, which was recently shown to also be required for micronemal trafficking of the TgMIC2 (T. gondii MIC2)-M2AP complex [Harper, Huynh, Coppens, Parussini, Moreno and Carruthers (2006) Mol. Biol. Cell 17, 4551-4563]. CONCLUSION Our results illuminate common and unique features of micronemal propeptides in their role as trafficking facilitators.
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