TY  - JOUR
A1  - Pawlowski, Nikolaus
A1  - Khaminets, Aliaksandr
A1  - Hunn, Julia
A1  - Papic, Natasa
A1  - Schmidt, Andreas
A1  - Uthaiah, Revathy Chottekalapanda
A1  - Lange, Rita
A1  - Vopper, Gabriela
A1  - Martens, Sascha
A1  - Wolf, Eva
A1  - Howard, Jonathan C.
T1  - The activation mechanism of Irga6, an interferon-inducible GTPase contributing to mouse resistance against Toxoplasma gondii
T2  - BMC Biology
N2  - Background: The 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. Results: Irga6 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 (SRalpha). 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. Conclusions: The 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.
Y1  - 2011
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/21061
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30-90382
N1  - © 2011 Pawlowski et al. ; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
VL  - 9
IS  - 7
ER  -