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Cabral G, Moss WJ, Brown KM. Proteomic approaches for protein kinase substrate identification in Apicomplexa. Mol Biochem Parasitol 2024; 259:111633. [PMID: 38821187 DOI: 10.1016/j.molbiopara.2024.111633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2024] [Revised: 05/10/2024] [Accepted: 05/28/2024] [Indexed: 06/02/2024]
Abstract
Apicomplexa is a phylum of protist parasites, notable for causing life-threatening diseases including malaria, toxoplasmosis, cryptosporidiosis, and babesiosis. Apicomplexan pathogenesis is generally a function of lytic replication, dissemination, persistence, host cell modification, and immune subversion. Decades of research have revealed essential roles for apicomplexan protein kinases in establishing infections and promoting pathogenesis. Protein kinases modify their substrates by phosphorylating serine, threonine, tyrosine, or other residues, resulting in rapid functional changes in the target protein. Post-translational modification by phosphorylation can activate or inhibit a substrate, alter its localization, or promote interactions with other proteins or ligands. Deciphering direct kinase substrates is crucial to understand mechanisms of kinase signaling, yet can be challenging due to the transient nature of kinase phosphorylation and potential for downstream indirect phosphorylation events. However, with recent advances in proteomic approaches, our understanding of kinase function in Apicomplexa has improved dramatically. Here, we discuss methods that have been used to identify kinase substrates in apicomplexan parasites, classifying them into three main categories: i) kinase interactome, ii) indirect phosphoproteomics and iii) direct labeling. We briefly discuss each approach, including their advantages and limitations, and highlight representative examples from the Apicomplexa literature. Finally, we conclude each main category by introducing prospective approaches from other fields that would benefit kinase substrate identification in Apicomplexa.
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Affiliation(s)
- Gabriel Cabral
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - William J Moss
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - Kevin M Brown
- Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA.
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Wang W, Yang Y, Guo H, Li MH, Chen XQ, Wei XY, Chen Y, Elsheikha HM, Zhang XX. Unravelling Strain-Specific Modifications of Toxoplasma gondii tRNA and sncRNA Using LC-MS/MS. Microbiol Spectr 2023; 11:e0356422. [PMID: 37036375 PMCID: PMC10269570 DOI: 10.1128/spectrum.03564-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Accepted: 03/21/2023] [Indexed: 04/11/2023] Open
Abstract
Many RNA modifications have been detected in rRNA, tRNA and small noncoding RNA (sncRNA) as well as in low-abundance RNA species such mRNA. Although RNA modifications play roles in many cellular and biological processes in various domains of life, knowledge about the diversity and role of RNA modifications in Toxoplasma gondii is limited. In this study, RNA modifications in three T. gondii strains (RH type I, PRU type II, and VEG type III) with distinct virulence abilities were determined by liquid chromatography-tandem mass spectrometry. We compared the levels of modifications of four nucleotides in tRNA and sncRNA, characterized RNA modification patterns of different T. gondii strains, and determined the diversity of RNA modifications. We detected and quantified 22 modified nucleosides in both tRNA and sncRNA. Significant differences in the diversity of the modified nucleosides were found between the three T. gondii strains. RNA modifications were correlated with the expression of many T. gondii virulence proteins. Some of the identified modifications (e.g., 2'-O-methylinosine, pseudouridine) play a role in mediating the host-parasite interaction. These results provide novel insight into the global modifications in tRNA and sncRNA, and the diversity of RNA modifications between T. gondii strains with different virulence backgrounds. IMPORTANCE Although RNA modifications play roles in many cellular and developmental processes in various domains of life, knowledge about the patterns and functions of RNA modifications in T. gondii is limited. Here, a quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach was used to study global RNA modifications in T. gondii strains of distinct virulence backgrounds. We quantified 22 modified nucleosides in both tRNA and sncRNA. Significant T. gondii strain-specific differences in RNA modifications were detected. More tRNA modifications correlated with T. gondii virulence proteins than sncRNA modifications. RNA modifications were significantly correlated with virulence proteins. Our data provide the first comprehensive profiling of the modifications tRNA and sncRNA in T. gondii, expanding the diversity of RNA modifications in this parasite and suggesting new regulators for modulating its virulence.
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Affiliation(s)
- Wei Wang
- College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, People’s Republic of China
- College of Animal Science and Veterinary Medicine, Heilongjiang Bayi Agriculture University, Daqing, People’s Republic of China
| | - Yi Yang
- College of Animal Sciences, Zhejiang Provincial Key Laboratory of Preventive Veterinary Medicine, Institute of Preventive Veterinary Medicine, Zhejiang University, Hangzhou, People’s Republic of China
| | - Huanping Guo
- Medical Center of Hematology, The Second Affiliated Hospital of Army Medical University, Chongqing, People’s Republic of China
| | - Ming-Han Li
- College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, People’s Republic of China
- College of Veterinary Medicine, Jilin Agricultural University, Changchun, People’s Republic of China
| | - Xiao-Qing Chen
- Jiangxi Provincial Key Laboratory for Animal Health, College of Animal Science and Technology, Jiangxi Agricultural University, Nanchang, People’s Republic of China
| | - Xin-Yu Wei
- College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, People’s Republic of China
- College of Animal Science and Veterinary Medicine, Heilongjiang Bayi Agriculture University, Daqing, People’s Republic of China
| | - Yu Chen
- College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, People’s Republic of China
- College of Animal Science and Veterinary Medicine, Heilongjiang Bayi Agriculture University, Daqing, People’s Republic of China
| | - Hany M. Elsheikha
- Faculty of Medicine and Health Sciences, School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Loughborough, United Kingdom
| | - Xiao-Xuan Zhang
- College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, People’s Republic of China
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Singh S, Murillo-León M, Endres NS, Arenas Soto AF, Gómez-Marín JE, Melbert F, Kanneganti TD, Yamamoto M, Campos C, Howard JC, Taylor GA, Steinfeldt T. ROP39 is an Irgb10-specific parasite effector that modulates acute Toxoplasma gondii virulence. PLoS Pathog 2023; 19:e1011003. [PMID: 36603017 PMCID: PMC9848475 DOI: 10.1371/journal.ppat.1011003] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Revised: 01/18/2023] [Accepted: 11/14/2022] [Indexed: 01/06/2023] Open
Abstract
Toxoplasma gondii (T. gondii) is a zoonotic apicomplexan parasite that is an important cause of clinical disability in humans. On a global scale, one third of the human population is infected with T. gondii. Mice and other small rodents are believed to be responsible for transmission of T. gondii to the domestic cat, its definitive host. Interferon-inducible Immunity-Related GTPases (IRG proteins) are important for control of murine T. gondii infections. Virulence differences between T. gondii strains are linked to polymorphic rhoptry proteins (ROPs) that cooperate to inactivate individual IRG family members. In particular, the pseudokinase ROP5 isoform B is critically important in laboratory strains of mice. We identified T. gondii ROP39 in complex with ROP5B and demonstrate its contribution to acute T. gondii virulence. ROP39 directly targets Irgb10 and inhibits homodimer formation of the GTPase leading to an overall reduction of IRG protein loading onto the parasitophorous vacuolar membrane (PVM). Maintenance of PVM integrity rescues the parasite from IRG protein-mediated clearance in vitro and in vivo. This study identifies a novel T. gondii effector that is important for specific inactivation of the IRG resistance system. Our data reveal that yet unknown T. gondii effectors can emerge from identification of direct interaction partners of ROP5B.
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Affiliation(s)
- Shishir Singh
- Institute of Virology, Medical Center University of Freiburg, Freiburg, Germany
- Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Mateo Murillo-León
- Institute of Virology, Medical Center University of Freiburg, Freiburg, Germany
- Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Niklas Sebastian Endres
- Institute of Virology, Medical Center University of Freiburg, Freiburg, Germany
- Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Ailan Farid Arenas Soto
- Grupo GEPAMOL, Centro de Investigaciones Biomedicas, Universidad del Quindio, Armenia, Quindio, Colombia
| | - Jorge Enrique Gómez-Marín
- Grupo GEPAMOL, Centro de Investigaciones Biomedicas, Universidad del Quindio, Armenia, Quindio, Colombia
| | - Florence Melbert
- Institute of Virology, Medical Center University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
| | - Thirumala-Devi Kanneganti
- Department of Immunology, St. Jude Children´s Research Hospital, Memphis, Tenessee, United States of America
| | - Masahiro Yamamoto
- Department of Immunoparasitology, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan
- Laboratory of Immunoparasitology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan
| | - Claudia Campos
- Fundacao Calouste Gulbekian, Instituto Gulbekian de Ciencia, Oeiras, Portugal
| | | | - Gregory Alan Taylor
- Departments of Medicine; Molecular Genetics and Microbiology; and Immunology; and Center for the Study of Aging and Human Development, Duke University Medical Center, Durham, North Carolina, United States of America
- Geriatric Research, Education, and Clinical Center, Durham VA Health Care System, Durham, North Carolina, United States of America
| | - Tobias Steinfeldt
- Institute of Virology, Medical Center University of Freiburg, Freiburg, Germany
- Faculty of Medicine, University of Freiburg, Freiburg, Germany
- * E-mail:
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Lim DC, Joukov V, Rettenmaier TJ, Kumagai A, Dunphy WG, Wells JA, Yaffe MB. Redox priming promotes Aurora A activation during mitosis. Sci Signal 2020; 13:eabb6707. [PMID: 32694171 PMCID: PMC8514121 DOI: 10.1126/scisignal.abb6707] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cell cycle-dependent redox changes can mediate transient covalent modifications of cysteine thiols to modulate the activities of regulatory kinases and phosphatases. Our previously reported finding that protein cysteine oxidation is increased during mitosis relative to other cell cycle phases suggests that redox modifications could play prominent roles in regulating mitotic processes. The Aurora family of kinases and their downstream targets are key components of the cellular machinery that ensures the proper execution of mitosis and the accurate segregation of chromosomes to daughter cells. In this study, x-ray crystal structures of the Aurora A kinase domain delineate redox-sensitive cysteine residues that, upon covalent modification, can allosterically regulate kinase activity and oligomerization state. We showed in both Xenopus laevis egg extracts and mammalian cells that a conserved cysteine residue within the Aurora A activation loop is crucial for Aurora A activation by autophosphorylation. We further showed that covalent disulfide adducts of this residue promote autophosphorylation of the Aurora A kinase domain. These findings reveal a potential mechanistic link between Aurora A activation and changes in the intracellular redox state during mitosis and provide insights into how novel small-molecule inhibitors may be developed to target specific subpopulations of Aurora A.
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Affiliation(s)
- Daniel C Lim
- MIT Center for Precision Cancer Medicine, Koch Institute for Integrative Cancer Research, and Departments of Biological Engineering and Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - Vladimir Joukov
- N. N. Petrov National Medical Research Center of Oncology, Saint Petersburg 197758, Russian Federation
| | - T Justin Rettenmaier
- Jnana Therapeutics, Boston, MA 02210, USA
- Departments of Pharmaceutical Chemistry and Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA 94158, USA
| | - Akiko Kumagai
- The Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - William G Dunphy
- The Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - James A Wells
- Departments of Pharmaceutical Chemistry and Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA 94158, USA
| | - Michael B Yaffe
- MIT Center for Precision Cancer Medicine, Koch Institute for Integrative Cancer Research, and Departments of Biological Engineering and Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
- Divisions of Acute Care Surgery, Trauma, and Surgical Critical Care, and Surgical Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
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Prediction of Toxoplasma gondii virulence factor ROP18 competitive inhibitors by virtual screening. Parasit Vectors 2019; 12:98. [PMID: 30867024 PMCID: PMC6416898 DOI: 10.1186/s13071-019-3341-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Accepted: 02/26/2019] [Indexed: 02/06/2023] Open
Abstract
Background Rhoptry protein 18 (ROP18) is a key virulence factor of Toxoplasma gondii. The host’s immune responses mediated by immune-related GTPases (IRGs) could be blocked by ROP18’s kinase activity. ROP18 also interacts with various substrates, such as activating transcription factor 6 beta (ATF6β) and affects multiple physiological functions within host cells, thereby inducing intense virulence. In this study, competitive inhibitors targeted to ROP18 were subjected to virtual screening based on the principle of structure-based drug design (SBDD). Methods The preparation of the ROP18 structure was conducted using the “Structure Prepare” function of Molecular Operating Environment (MOE) software. The ATP-binding pocket was selected as the starting point for virtual screening. Construction of the pharmacophore model used Extended Hückel Theory (EHT) half-quantitative measurement and construction, as well as the characteristics of Type I kinase inhibitors. The pharmacophore model of ROP18 was imported into the Specs database for small molecule similarity screening using EHT pharmacophore measurement. Hit compounds were selected using the functions of London dG and generalized-born volume integral/weighted surface area (GBVI/WSA) scoring. The top 100 hits were analyzed by molecular docking and structure activity relationships (SAR) analysis. Results The final pharmacophore comprised three typical characteristics: three hydrogen bond acceptors/donors, two ring aromatic features occupying the hydrophobic core, and one cation group feature targeted to the terminus of ATP. A total of 1314 hit compounds analogous to ROP18 pharmacophore were passed through the Specs. After two rounds of docking, 25 out of 100 hits were identified as belonging to two main scaffold types: phthalimide ring structure, thiazole ring and styrene structure. Additionally, the screen also identified 13 inhibitors with distinct scaffold types. The docking models and SAR analysis demonstrated that these hits could engage in multiple hydrogen bonds, salt bridges halogen bonds, and hydrophobic interactions with ROP18, and para-position halo substituents on the benzene ring may enhance their affinity scoring. Conclusions A pharmacophore against the ROP18 ATP-binding pocket was successfully constructed, and 25 representative inhibitors from 15 scaffold clusters were screened using the Specs database. Our results provide useful scaffold types for the chemical inhibition of ROP18 or alternative conformations to develop new anti-toxoplasmosis drug leads. Electronic supplementary material The online version of this article (10.1186/s13071-019-3341-y) contains supplementary material, which is available to authorized users.
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Protein targets of thiazolidinone derivatives in Toxoplasma gondii and insights into their binding to ROP18. BMC Genomics 2018; 19:856. [PMID: 30497375 PMCID: PMC6267824 DOI: 10.1186/s12864-018-5223-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2018] [Accepted: 11/05/2018] [Indexed: 01/20/2023] Open
Abstract
Background Thiazolidinone derivatives show inhibitory activity (IC50) against the Toxoplasma gondii parasite, as well as high selectivity with high therapeutic index. To disclose the target proteins of the thiazolidinone core in this parasite, we explored in silico the active sites of different T. gondii proteins and estimated the binding-free energy of reported thiazolidinone molecules with inhibitory effect on invasion and replication of the parasite inside host cells. This enabled us to describe some of the most suitable structural characteristics to design a compound derived from the thiazolidinone core. Results The best binding affinity was observed in the active site of kinase proteins, we selected the active site of the T. gondii ROP18 kinase, because it is an important factor for the virulence and survival of the parasite. We present the possible effect of a derivative of thiazolidinone core in the active site of T. gondii ROP18 and described some characteristics of substituent groups that could improve the affinity and specificity of compounds derived from the thiazolidinone core against T. gondii. Conclusions The results of our study suggest that compounds derived from the thiazolidinone core have a preference for protein kinases of T. gondii, being promising compounds for the development of new drugs with potential anti-toxoplasmosis activity. Our findings highlight the importance of use computational studies for the understanding of the action mechanism of compounds with biological activity. Electronic supplementary material The online version of this article (10.1186/s12864-018-5223-7) contains supplementary material, which is available to authorized users.
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The Toxoplasma Parasitophorous Vacuole: An Evolving Host-Parasite Frontier. Trends Parasitol 2017; 33:473-488. [PMID: 28330745 DOI: 10.1016/j.pt.2017.02.007] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 02/20/2017] [Accepted: 02/24/2017] [Indexed: 01/17/2023]
Abstract
The parasitophorous vacuole is a unique replicative niche for apicomplexan parasites, including Toxoplasma gondii. Derived from host plasma membrane, the vacuole is rendered nonfusogenic with the host endolysosomal system. Toxoplasma secretes numerous proteins to modify the forming vacuole, enable nutrient uptake, and set up mechanisms of host subversion. Here we describe the pathways of host-parasite interaction at the parasitophorous vacuole employed by Toxoplasma and host, leading to the intricate balance of host defence versus parasite survival.
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Yang Z, Hou Y, Hao T, Rho HS, Wan J, Luan Y, Gao X, Yao J, Pan A, Xie Z, Qian J, Liao W, Zhu H, Zhou X. A Human Proteome Array Approach to Identifying Key Host Proteins Targeted by Toxoplasma Kinase ROP18. Mol Cell Proteomics 2017; 16:469-484. [PMID: 28087594 DOI: 10.1074/mcp.m116.063602] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2016] [Revised: 12/20/2016] [Indexed: 12/18/2022] Open
Abstract
Toxoplasma kinase ROP18 is a key molecule responsible for the virulence of Toxoplasma gondii; however, the mechanisms by which ROP18 exerts parasite virulence via interaction with host proteins remain limited to a small number of identified substrates. To identify a broader array of ROP18 substrates, we successfully purified bioactive mature ROP18 and used it to probe a human proteome array. Sixty eight new putative host targets were identified. Functional annotation analysis suggested that these proteins have a variety of functions, including metabolic process, kinase activity and phosphorylation, cell growth, apoptosis and cell death, and immunity, indicating a pleiotropic role of ROP18 kinase. Among these proteins, four candidates, p53, p38, UBE2N, and Smad1, were further validated. We demonstrated that ROP18 targets p53, p38, UBE2N, and Smad1 for degradation. Importantly, we demonstrated that ROP18 phosphorylates Smad1 Ser-187 to trigger its proteasome-dependent degradation. Further functional characterization of the substrates of ROP18 may enhance understanding of the pathogenesis of Toxoplasma infection and provide new therapeutic targets. Similar strategies could be used to identify novel host targets for other microbial kinases functioning at the pathogen-host interface.
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Affiliation(s)
- Zhaoshou Yang
- From the ‡Department of Biochemistry and Molecular Biology, Sun Yat-Sen University Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou 510080, China
| | - Yongheng Hou
- From the ‡Department of Biochemistry and Molecular Biology, Sun Yat-Sen University Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou 510080, China
| | - Taofang Hao
- From the ‡Department of Biochemistry and Molecular Biology, Sun Yat-Sen University Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou 510080, China
| | - Hee-Sool Rho
- the §Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Jun Wan
- the ¶Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287
| | - Yizhao Luan
- the ‖State Key Lab of Ophthalmology, Guangdong Provincial Key Lab of Ophthalmology and Visual Science, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou 510060, China.,the **School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Xin Gao
- ‡‡The Third Affiliated Hospital, Sun Yat-Sen University, Guangzhou 510630, China; and
| | - Jianping Yao
- §§The First Affiliated Hospital, Sun Yat-Sen University, Guangzhou 510080, China
| | - Aihua Pan
- From the ‡Department of Biochemistry and Molecular Biology, Sun Yat-Sen University Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou 510080, China
| | - Zhi Xie
- the ‖State Key Lab of Ophthalmology, Guangdong Provincial Key Lab of Ophthalmology and Visual Science, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou 510060, China
| | - Jiang Qian
- the ¶Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287
| | - Wanqin Liao
- From the ‡Department of Biochemistry and Molecular Biology, Sun Yat-Sen University Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou 510080, China;
| | - Heng Zhu
- the §Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205;
| | - Xingwang Zhou
- From the ‡Department of Biochemistry and Molecular Biology, Sun Yat-Sen University Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou 510080, China;
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Haubrich BA, Swinney DC. Enzyme Activity Assays for Protein Kinases: Strategies to Identify Active Substrates. Curr Drug Discov Technol 2016; 13:2-15. [PMID: 26768716 DOI: 10.2174/1570163813666160115125930] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 01/13/2016] [Accepted: 01/13/2016] [Indexed: 11/22/2022]
Abstract
Protein kinases are an important class of enzymes and drug targets. New opportunities to discover medicines for neglected diseases can be leveraged by the extensive kinase tools and knowledge created in targeting human kinases. A valuable tool for kinase drug discovery is an enzyme assay that measures catalytic function. The functional assay can be used to identify inhibitors, estimate affinity, characterize molecular mechanisms of action (MMOAs) and evaluate selectivity. However, establishing an enzyme assay for a new kinases requires identification of a suitable substrate. Identification of a new kinase's endogenous physiologic substrate and function can be extremely costly and time consuming. Fortunately, most kinases are promiscuous and will catalyze the phosphotransfer from ATP to alternative substrates with differing degrees of catalytic efficiency. In this manuscript we review strategies and successes in the identification of alternative substrates for kinases from organisms responsible for many of the neglected tropical diseases (NTDs) towards the goal of informing strategies to identify substrates for new kinases. Approaches for establishing a functional kinase assay include measuring auto-activation and use of generic substrates and peptides. The most commonly used generic substrates are casein, myelin basic protein, and histone. Sequence homology modeling can provide insights into the potential substrates and the requirement for activation. Empirical approaches that can identify substrates include screening of lysates (which may also help identify native substrates) and use of peptide arrays. All of these approaches have been used with a varying degree of success to identify alternative substrates.
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Affiliation(s)
- Brad A Haubrich
- Institute for Rare and Neglected Diseases Drug Discovery, 897 Independence Ave, Suite 2C, Mountain View, CA 94043, USA.
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Pilla-Moffett D, Barber MF, Taylor GA, Coers J. Interferon-Inducible GTPases in Host Resistance, Inflammation and Disease. J Mol Biol 2016; 428:3495-513. [PMID: 27181197 DOI: 10.1016/j.jmb.2016.04.032] [Citation(s) in RCA: 144] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 04/23/2016] [Accepted: 04/30/2016] [Indexed: 01/18/2023]
Abstract
Cell-autonomous immunity is essential for host organisms to defend themselves against invasive microbes. In vertebrates, both the adaptive and the innate branches of the immune system operate cell-autonomous defenses as key effector mechanisms that are induced by pro-inflammatory interferons (IFNs). IFNs can activate cell-intrinsic host defenses in virtually any cell type ranging from professional phagocytes to mucosal epithelial cells. Much of this IFN-induced host resistance program is dependent on four families of IFN-inducible GTPases: the myxovirus resistance proteins, the immunity-related GTPases, the guanylate-binding proteins (GBPs), and the very large IFN-inducible GTPases. These GTPase families provide host resistance to a variety of viral, bacterial, and protozoan pathogens through the sequestration of microbial proteins, manipulation of vesicle trafficking, regulation of antimicrobial autophagy (xenophagy), execution of intracellular membranolytic pathways, and the activation of inflammasomes. This review discusses our current knowledge of the molecular function of IFN-inducible GTPases in providing host resistance, as well as their role in the pathogenesis of autoinflammatory Crohn's disease. While substantial advances were made in the recent past, few of the known functions of IFN-inducible GTPases have been explored in any depth, and new functions await discovery. This review will therefore highlight key areas of future exploration that promise to advance our understanding of the role of IFN-inducible GTPases in human diseases.
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Affiliation(s)
- Danielle Pilla-Moffett
- Department of Molecular Genetics and Microbiology, and Immunology, Duke University Medical Center, Durham, NC 27710, USA
| | - Matthew F Barber
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, UT 84112, USA
| | - Gregory A Taylor
- Department of Medicine, Duke University, Durham, NC 27708, USA; Department of Molecular Genetics and Microbiology, and Immunology, Duke University, Durham, NC 27708, USA; Center for the Study of Aging, Duke University, Durham, NC 27708, USA; Geriatric Research and Education and Clinical Center, Veteran Affairs Medical Center, Durham, NC 27710, USA.
| | - Jörn Coers
- Department of Molecular Genetics and Microbiology, and Immunology, Duke University Medical Center, Durham, NC 27710, USA.
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Abstract
Ingestion of the obligate intracellular protozoan parasite Toxoplasma gondii causes an acute infection that leads to chronic infection of the host. To facilitate the acute phase of the infection, T. gondii manipulates the host response by secreting rhoptry organelle proteins (ROPs) into host cells during its invasion. A few key ROP proteins with signatures of kinases or pseudokinases (ROPKs) act as virulence factors that enhance parasite survival against host gamma interferon-stimulated innate immunity. However, the roles of these and other ROPK proteins in establishing chronic infection have not been tested. Here, we deleted 26 ROPK gene loci encoding 31 unique ROPK proteins of type II T. gondii and show that numerous ROPK proteins influence the development of chronic infection. Cyst burdens were increased in the Δrop16 knockout strain or moderately reduced in 11 ROPK knockout strains. In contrast, deletion of ROP5, ROP17, ROP18, ROP35, or ROP38/29/19 (ROP38, ROP29, and ROP19) severely reduced cyst burdens. Δrop5 and Δrop18 knockout strains were less resistant to host immunity-related GTPases (IRGs) and exhibited >100-fold-reduced virulence. ROP18 kinase activity and association with the parasitophorous vacuole membrane were necessary for resistance to host IRGs. The Δrop17 strain exhibited a >12-fold defect in virulence; however, virulence was not affected in the Δrop35 or Δrop38/29/19 strain. Resistance to host IRGs was not affected in the Δrop17, Δrop35, or Δrop38/29/19 strain. Collectively, these findings provide the first definitive evidence that the type II T. gondii ROPK proteome functions as virulence factors and facilitates additional mechanisms of host manipulation that are essential for chronic infection and transmission of T. gondii. Reactivation of chronic Toxoplasma gondii infection in individuals with weakened immune systems causes severe toxoplasmosis. Existing treatments for toxoplasmosis are complicated by adverse reactions to chemotherapy. Understanding key parasite molecules required for chronic infection provides new insights into potential mechanisms that can interrupt parasite survival or persistence in the host. This study reveals that key secreted rhoptry molecules are used by the parasite to establish chronic infection of the host. Certain rhoptry proteins were found to be critical virulence factors that resist innate immunity, while other rhoptry proteins were found to influence chronic infection without affecting virulence. This study reveals that rhoptry proteins utilize multiple mechanisms of host manipulation to establish chronic infection of the host. Targeted disruption of parasite rhoptry proteins involved in these biological processes opens new avenues to interfere with chronic infection with the goal to either eliminate chronic infection or to prevent recrudescent infections.
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12
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Simpson C, Jones NG, Hull-Ryde EA, Kireev D, Stashko M, Tang K, Janetka J, Wildman SA, Zuercher WJ, Schapira M, Hui R, Janzen W, Sibley LD. Identification of small molecule inhibitors that block the Toxoplasma gondii rhoptry kinase ROP18. ACS Infect Dis 2016; 2:194-206. [PMID: 27379343 PMCID: PMC4930114 DOI: 10.1021/acsinfecdis.5b00102] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The protozoan parasite Toxoplasma gondii secretes a family of serine-threonine protein kinases into its host cell in order to disrupt signaling and alter immune responses. One prominent secretory effector is the rhoptry protein 18 (ROP18), a serine-threonine kinase that phosphorylates immunity related GTPases (IRGs) and hence blocks interferon gamma-mediated responses in rodent cells. Previous genetic studies show that ROP18 is a major virulence component of T. gondii strains from North and South America. Here, we implemented a high throughput screen to identify small molecule inhibitors of ROP18 in vitro and subsequently validated their specificity within infected cells. Although ROP18 was not susceptible to many kinase-directed inhibitors that affect mammalian kinases, the screen identified several sub micromolar inhibitors that belong to three chemical scaffolds: oxindoles, 6-azaquinazolines, and pyrazolopyridines. Treatment of interferon gamma-activated cells with one of these inhibitors enhanced immunity related GTPase recruitment to wild type parasites, recapitulating the defect of Δrop18 mutant parasites, consistent with targeting ROP18 within infected cells. These compounds provide useful starting points for chemical biology experiments or as leads for therapeutic interventions designed to reduce parasite virulence.
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Affiliation(s)
- Catherine Simpson
- Center for Integrative Chemical Biology and Drug Discovery, UNC
Eshelman School of Pharmacy, University of North Carolina, 125 Mason Farm Road,
CB#7363, Chapel Hill, NC 27599-7363
| | - Nathaniel G. Jones
- Department of Molecular Microbiology, Washington University Sch.
Med. St. Louis MO 63110
| | - Emily A. Hull-Ryde
- Center for Integrative Chemical Biology and Drug Discovery, UNC
Eshelman School of Pharmacy, University of North Carolina, 125 Mason Farm Road,
CB#7363, Chapel Hill, NC 27599-7363
| | - Dmitri Kireev
- Center for Integrative Chemical Biology and Drug Discovery, UNC
Eshelman School of Pharmacy, University of North Carolina, 125 Mason Farm Road,
CB#7363, Chapel Hill, NC 27599-7363
| | - Michael Stashko
- Center for Integrative Chemical Biology and Drug Discovery, UNC
Eshelman School of Pharmacy, University of North Carolina, 125 Mason Farm Road,
CB#7363, Chapel Hill, NC 27599-7363
| | - Keliang Tang
- Department of Molecular Microbiology, Washington University Sch.
Med. St. Louis MO 63110
| | - Jim Janetka
- Department of Biochemistry and Molecular Biophysics, Washington
University Sch. Med. St. Louis MO 63110
| | - Scott A. Wildman
- Department of Biochemistry and Molecular Biophysics, Washington
University Sch. Med. St. Louis MO 63110
| | - William J. Zuercher
- SGC-UNC, Division of Chemical Biology and Medicinal Chemistry, UNC
Eshelman School of Pharmacy, 120 Mason Farm Rd, 1070H Genetic Medicine Building,
University of North Carolina, NC 27599-7363
| | - Matthieu Schapira
- Structural Genomics Consortium, University of Toronto, MaRS South
Tower, 101 College St, Toronto, ON, M5G 1L7, Canada
- Department of Pharmacology and Toxicology, University of Toronto, 1
King’s College Circle, Toronto, ON M5S 1A8, Canada
| | - Raymond Hui
- Structural Genomics Consortium, University of Toronto, MaRS South
Tower, 101 College St, Toronto, ON, M5G 1L7, Canada
- Toronto General Hospital Research Institute, 200 Elizabeth St.,
Toronto, ON M5G 2C4, Canada
| | - William Janzen
- Center for Integrative Chemical Biology and Drug Discovery, UNC
Eshelman School of Pharmacy, University of North Carolina, 125 Mason Farm Road,
CB#7363, Chapel Hill, NC 27599-7363
| | - L. David Sibley
- Department of Molecular Microbiology, Washington University Sch.
Med. St. Louis MO 63110
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Cabral CM, Tuladhar S, Dietrich HK, Nguyen E, MacDonald WR, Trivedi T, Devineni A, Koshy AA. Neurons are the Primary Target Cell for the Brain-Tropic Intracellular Parasite Toxoplasma gondii. PLoS Pathog 2016; 12:e1005447. [PMID: 26895155 PMCID: PMC4760770 DOI: 10.1371/journal.ppat.1005447] [Citation(s) in RCA: 120] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Accepted: 01/19/2016] [Indexed: 11/17/2022] Open
Abstract
Toxoplasma gondii, a common brain-tropic parasite, is capable of infecting most nucleated cells, including astrocytes and neurons, in vitro. Yet, in vivo, Toxoplasma is primarily found in neurons. In vitro data showing that interferon-γ-stimulated astrocytes, but not neurons, clear intracellular parasites suggest that neurons alone are persistently infected in vivo because they lack the ability to clear intracellular parasites. Here we test this theory by using a novel Toxoplasma-mouse model capable of marking and tracking host cells that directly interact with parasites, even if the interaction is transient. Remarkably, we find that Toxoplasma shows a strong predilection for interacting with neurons throughout CNS infection. This predilection remains in the setting of IFN-γ depletion; infection with parasites resistant to the major mechanism by which murine astrocytes clear parasites; or when directly injecting parasites into the brain. These findings, in combination with prior work, strongly suggest that neurons are not incidentally infected, but rather they are Toxoplasma's primary in vivo target.
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Affiliation(s)
- Carla M Cabral
- BIO5 Institute, University of Arizona, Tucson, Arizona, United States of America
| | - Shraddha Tuladhar
- Department of Immunobiology, University of Arizona, Tucson, Arizona, United States of America
| | - Hans K Dietrich
- BIO5 Institute, University of Arizona, Tucson, Arizona, United States of America
| | - Elizabeth Nguyen
- BIO5 Institute, University of Arizona, Tucson, Arizona, United States of America
| | - Wes R MacDonald
- Undergraduate Biology Research Program, University of Arizona, Tucson, Arizona, United States of America
| | - Tapasya Trivedi
- BIO5 Institute, University of Arizona, Tucson, Arizona, United States of America
| | - Asha Devineni
- BIO5 Institute, University of Arizona, Tucson, Arizona, United States of America
| | - Anita A Koshy
- BIO5 Institute, University of Arizona, Tucson, Arizona, United States of America.,Department of Immunobiology, University of Arizona, Tucson, Arizona, United States of America.,Department of Neurology, University of Arizona, Tucson, Arizona, United States of America
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Hermanns T, Müller UB, Könen-Waisman S, Howard JC, Steinfeldt T. The Toxoplasma gondii rhoptry protein ROP18 is an Irga6-specific kinase and regulated by the dense granule protein GRA7. Cell Microbiol 2015; 18:244-59. [PMID: 26247512 PMCID: PMC5061101 DOI: 10.1111/cmi.12499] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2015] [Revised: 07/29/2015] [Accepted: 07/29/2015] [Indexed: 01/05/2023]
Abstract
In mice, avirulent strains (e.g. types II and III) of the protozoan parasite Toxoplasma gondii are restricted by the immunity‐related GTPase (IRG) resistance system. Loading of IRG proteins onto the parasitophorous vacuolar membrane (PVM) is required for vacuolar rupture resulting in parasite clearance. In virulent strain (e.g. type I) infections, polymorphic effector proteins ROP5 and ROP18 cooperate to phosphorylate and thereby inactivate mouse IRG proteins to preserve PVM integrity. In this study, we confirmed the dense granule protein GRA7 as an additional component of the ROP5/ROP18 kinase complex and identified GRA7 association with the PVM by direct binding to ROP5. The absence of GRA7 results in reduced phosphorylation of Irga6 correlated with increased vacuolar IRG protein amounts and attenuated virulence. Earlier work identified additional IRG proteins as targets of T. gondii ROP18 kinase. We show that the only specific target of ROP18 among IRG proteins is in fact Irga6. Similarly, we demonstrate that GRA7 is strictly an Irga6‐specific virulence effector. This identifies T. gondii GRA7 as a regulator for ROP18‐specific inactivation of Irga6. The structural diversity of the IRG proteins implies that certain family members constitute additional specific targets for other yet unknown T. gondii virulence effectors.
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Affiliation(s)
- Thomas Hermanns
- Institute for Genetics, University of Cologne, Cologne, Germany
| | - Urs B Müller
- Institute for Genetics, University of Cologne, Cologne, Germany
| | | | - Jonathan C Howard
- Fundação Calouste Gulbenkian, Instituto Gulbenkian de Ciência, Oeiras, Portugal
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Biochemical characterization of FIKK8--A unique protein kinase from the malaria parasite Plasmodium falciparum and other apicomplexans. Mol Biochem Parasitol 2015; 201:85-9. [PMID: 26112892 PMCID: PMC4576209 DOI: 10.1016/j.molbiopara.2015.06.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 05/21/2015] [Accepted: 06/08/2015] [Indexed: 11/24/2022]
Abstract
We studied FIKK kinases from Plasmodium falciparum and Cryptosporidium parvum. Soluble and active samples of PfFIKK8 and CpFIKK contain a N-terminal extension. Both FIKK samples preferentially phosphorylated serines with flanking arginines.
FIKKs are protein kinases with distinctive sequence motifs found exclusively in Apicomplexa. Here, we report on the biochemical characterization of Plasmodium falciparum FIKK8 (PfFIKK8) and its Cryptosporidium parvum orthologue (CpFIKK) – the only member of the family predicted to be cytosolic and conserved amongst non-Plasmodium parasites. Recombinant protein samples of both were catalytically active. We characterized their phosphorylation ability using an enzymatic assay and substrate specificities using an arrayed positional scanning peptide library. Our results show that FIKK8 targets serine, preferably with arginine in the +3 and −3 positions. Furthermore, the soluble and active FIKK constructs in our experiments contained an N-terminal extension (NTE) conserved in FIKK8 orthologues from other apicomplexan species. Based on our results, we propose that this NTE is an integral feature of the FIKK subfamily.
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Li XZ, Wang XH, Xia LJ, Weng YB, Hernandez JA, Tu LQ, Li LT, Li SJ, Yuan ZG. Protective efficacy of recombinant canine adenovirus type-2 expressing TgROP18 (CAV-2-ROP18) against acute and chronic Toxoplasma gondii infection in mice. BMC Infect Dis 2015; 15:114. [PMID: 25886737 PMCID: PMC4397727 DOI: 10.1186/s12879-015-0815-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 02/09/2015] [Indexed: 12/31/2022] Open
Abstract
Background The use of recombinant viral vectors expressing T. gondii antigens is a safe and efficient approach to induce immune responses against the parasite, as well as a valuable tool for vaccine development. We have previously prolonged the survival time of mice challenged with the RH strain of T. gondii by immunizing the mice with a eukaryotic vector expressing the protein ROP18 of T. gondii. We are now looking for ways to improve this vaccination strategy and enhance protection. Methods In this study, we constructed and characterized a novel recombinant canine adenovirus type 2 expressing ROP18 (CAV-2-ROP18) of T. gondii by cytopathic effect (CPE) and indirect immunofluorescence assay (IFA) following transfection into MDCK cells. Intramuscular immunization of Kunming mice with CAV-2-ROP18 was carried out to evaluate humoral and cellular immune responses. Results The vaccination of experimental mice with CAV-2-ROP18 elicited antibody production against ROP18, including high levels of a mixed IgG1/IgG2a and significant production of IFN-γ or IL-2, and displayed a significant bias towards a helper T cell type 1 (Th1) profile. Furthermore, the presence of T. gondii-specific IFN-γ-production and TNF-α-production T cells was elicited in both CD4+ and CD8+ T cell compartments. Significantly higher survival rates (40%) occurred in the experimental group, and a reduction in brain cyst burden was detected in vaccinated mice. Conclusion These results demonstrate the potential use of a CAV vector harboring the ROP18 gene in the development of a vaccine against acute and chronic toxoplasmosis. Electronic supplementary material The online version of this article (doi:10.1186/s12879-015-0815-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Xiu-Zhen Li
- College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, PR China. .,Guangdong Provincial Key Laboratory of Prevention and Control for Severe Clinical Animal Diseases, Guangzhou, Guangdong Province, 510642, PR China.
| | - Xiao-Hu Wang
- Institute of Animal Health, Guangdong Academy of Agricultural Sciences, Guangzhou, Guangdong Province, 510642, PR China.
| | - Li-Jun Xia
- College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, PR China. .,Guangdong Provincial Key Laboratory of Prevention and Control for Severe Clinical Animal Diseases, Guangzhou, Guangdong Province, 510642, PR China.
| | - Ya-Biao Weng
- College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, PR China.
| | - Jorge A Hernandez
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA.
| | - Li-Qing Tu
- College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, PR China. .,Guangdong Provincial Key Laboratory of Prevention and Control for Severe Clinical Animal Diseases, Guangzhou, Guangdong Province, 510642, PR China.
| | - Lu-Tao Li
- College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, PR China. .,Guangdong Provincial Key Laboratory of Prevention and Control for Severe Clinical Animal Diseases, Guangzhou, Guangdong Province, 510642, PR China.
| | - Shou-Jun Li
- College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, PR China. .,Guangdong Provincial Key Laboratory of Prevention and Control for Severe Clinical Animal Diseases, Guangzhou, Guangdong Province, 510642, PR China.
| | - Zi-Guo Yuan
- College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province, 510642, PR China. .,Guangdong Provincial Key Laboratory of Prevention and Control for Severe Clinical Animal Diseases, Guangzhou, Guangdong Province, 510642, PR China.
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Toxoplasma gondii superinfection and virulence during secondary infection correlate with the exact ROP5/ROP18 allelic combination. mBio 2015; 6:e02280. [PMID: 25714710 PMCID: PMC4358003 DOI: 10.1128/mbio.02280-14] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The intracellular parasite Toxoplasma gondii infects a wide variety of vertebrate species globally. Infection in most hosts causes a lifelong chronic infection and generates immunological memory responses that protect the host against new infections. In regions where the organism is endemic, multiple exposures to T. gondii likely occur with great frequency, yet little is known about the interaction between a chronically infected host and the parasite strains from these areas. A widely used model to explore secondary infection entails challenge of chronically infected or vaccinated mice with the highly virulent type I RH strain. Here, we show that although vaccinated or chronically infected C57BL/6 mice are protected against the type I RH strain, they are not protected against challenge with most strains prevalent in South America or another type I strain, GT1. Genetic and genomic analyses implicated the parasite-secreted rhoptry effectors ROP5 and ROP18, which antagonize the host’s gamma interferon-induced immunity-regulated GTPases (IRGs), as primary requirements for virulence during secondary infection. ROP5 and ROP18 promoted parasite superinfection in the brains of challenged survivors. We hypothesize that superinfection may be an important mechanism to generate T. gondii strain diversity, simply because two parasite strains would be present in a single meal consumed by the feline definitive host. Superinfection may drive the genetic diversity of Toxoplasma strains in South America, where most isolates are IRG resistant, compared to North America, where most strains are IRG susceptible and are derived from a few clonal lineages. In summary, ROP5 and ROP18 promote Toxoplasma virulence during reinfection. Toxoplasma gondii is a widespread parasite of warm-blooded animals and currently infects one-third of the human population. A long-standing assumption in the field is that prior exposure to this parasite protects the host from subsequent reexposure, due to the generation of protective immunological memory. However, this assumption is based on clinical data and mouse models that analyze infections with strains common to Europe and North America. In contrast, we found that the majority of strains sampled from around the world, in particular those from South America, were able to kill or reinfect the brains of hosts previously exposed to T. gondii. The T. gondii virulence factors ROP5 and ROP18, which inhibit key host effectors that mediate parasite killing, were required for these phenotypes. We speculate that these results underpin clinical observations that pregnant women previously exposed to Toxoplasma can develop congenital infection upon reexposure to South American strains.
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