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Inactive and active states of the interferon-inducible resistance GTPase, Irga6, in vivo.

ABSTRACT: Irga6, a myristoylated, interferon-inducible member of the immunity-related GTPase family, contributes to disease resistance against Toxoplasma gondii in mice. Accumulation of Irga6 on the T. gondii parasitophorous vacuole membrane is associated with vesiculation and ultimately disruption of the vacuolar membrane in a process that requires an intact GTP-binding domain. The role of the GTP-binding domain of Irga6 in pathogen resistance is, however, unclear. We provide evidence that Irga6 in interferon-induced, uninfected cells is predominantly in a GDP-bound state that is maintained by other interferon-induced proteins. However, Irga6 that accumulates on the parasitophorous vacuole membrane after Toxoplasma infection is in the GTP-bound form. We demonstrate that a monoclonal antibody, 10D7, specifically detects GTP-bound Irga6, and we show that the formation of the 10D7 epitope follows from a GTP-dependent conformational transition of the N terminus of Irga6, anticipating an important role of the myristoyl group on Irga6 function in vivo.

SUBMITTER: Papic N

PROVIDER: S-EPMC2581590 | biostudies-literature | 2008 Nov

REPOSITORIES: biostudies-literature

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Inactive and active states of the interferon-inducible resistance GTPase, Irga6, in vivo.

Papic Natasa N Hunn Julia P JP Pawlowski Nikolaus N Zerrahn Jens J Howard Jonathan C JC

The Journal of biological chemistry 20080910 46

Irga6, a myristoylated, interferon-inducible member of the immunity-related GTPase family, contributes to disease resistance against Toxoplasma gondii in mice. Accumulation of Irga6 on the T. gondii parasitophorous vacuole membrane is associated with vesiculation and ultimately disruption of the vacuolar membrane in a process that requires an intact GTP-binding domain. The role of the GTP-binding domain of Irga6 in pathogen resistance is, however, unclear. We provide evidence that Irga6 in inter ...[more]

PMID: 18784077

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Project description:BackgroundThe interferon-inducible immunity-related GTPases (IRG proteins/p47 GTPases) are a distinctive family of GTPases that function as powerful cell-autonomous resistance factors. The IRG protein, Irga6 (IIGP1), participates in the disruption of the vacuolar membrane surrounding the intracellular parasite, Toxoplasma gondii, through which it communicates with its cellular hosts. Some aspects of the protein's behaviour have suggested a dynamin-like molecular mode of action, in that the energy released by GTP hydrolysis is transduced into mechanical work that results in deformation and ultimately rupture of the vacuolar membrane.ResultsIrga6 forms GTP-dependent oligomers in vitro and thereby activates hydrolysis of the GTP substrate. In this study we define the catalytic G-domain interface by mutagenesis and present a structural model, of how GTP hydrolysis is activated in Irga6 complexes, based on the substrate-twinning reaction mechanism of the signal recognition particle (SRP) and its receptor (SRα). In conformity with this model, we show that the bound nucleotide is part of the catalytic interface and that the 3'hydroxyl of the GTP ribose bound to each subunit is essential for trans-activation of hydrolysis of the GTP bound to the other subunit. We show that both positive and negative regulatory interactions between IRG proteins occur via the catalytic interface. Furthermore, mutations that disrupt the catalytic interface also prevent Irga6 from accumulating on the parasitophorous vacuole membrane of T. gondii, showing that GTP-dependent Irga6 activation is an essential component of the resistance mechanism.ConclusionsThe catalytic interface of Irga6 defined in the present experiments can probably be used as a paradigm for the nucleotide-dependent interactions of all members of the large family of IRG GTPases, both activating and regulatory. Understanding the activation mechanism of Irga6 will help to explain the mechanism by which IRG proteins exercise their resistance function. We find no support from sequence or G-domain structure for the idea that IRG proteins and the SRP GTPases have a common phylogenetic origin. It therefore seems probable, if surprising, that the substrate-assisted catalytic mechanism has been independently evolved in the two protein families.

Project description:BackgroundMigraine is a very common headache disorder on the population level, characterized by symptomatic attacks (activity). For many people with migraine, the migraine symptoms intermittently or permanently cease during their lifetime (inactive migraine). The current diagnostic classification of migraine considers two states: active migraine (having migraine symptoms within the last year) and not having active migraine (including both individuals with inactive migraine and those who never had migraine). Defining a state of inactive migraine that has gone into remission may better capture the trajectories of migraine across the lifespan and contribute to a better understanding of its biological processes. We aimed to quantify the prevalence of never, active, and inactive migraine separately, using modern prevalence and incidence estimation methodology to better describe the complexity of migraine trajectories at the population level.MethodsUsing a multistate modeling approach, data from the Global Burden of Disease (GBD) study, and results from a population-based study, we estimated the transition rates by which individuals moved between migraine disease states and estimated prevalences of never, active and inactive migraine. We used data from the GBD project and a hypothetical cohort of 100,000 people with a starting age of 30 and 30 years of follow-up, both in Germany and globally, stratified by sex.ResultsIn Germany, the estimated rate of transition from active to inactive migraine (remission rate) increased after the age of 22.5 in women and 27.5 in men. The pattern for men in Germany was similar to the one observed on the global level. The prevalence of inactive migraine among women reaches 25.7% in Germany and 16.5% globally at age 60. For men, the inactive migraine prevalence estimates at the same age were 10.4% in Germany and 7.1% globally.ConclusionsConsidering an inactive migraine state explicitly reflects a different epidemiological picture of migraine across the lifecourse. We have demonstrated that many women of older ages may be in an inactive migraine state. Many pressing research questions can only be answered if population-based cohort studies collect information not only on active migraine but also on inactive migraine states.

Dataset Information

Inactive and active states of the interferon-inducible resistance GTPase, Irga6, in vivo.

Publications

Inactive and active states of the interferon-inducible resistance GTPase, Irga6, in vivo.

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