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Structural and functional insights into the mode of action of a universally conserved Obg GTPase.

ABSTRACT: Obg proteins are a family of P-loop GTPases, conserved from bacteria to human. The Obg protein in Escherichia coli (ObgE) has been implicated in many diverse cellular functions, with proposed molecular roles in two global processes, ribosome assembly and stringent response. Here, using pre-steady state fast kinetics we demonstrate that ObgE is an anti-association factor, which prevents ribosomal subunit association and downstream steps in translation by binding to the 50S subunit. ObgE is a ribosome dependent GTPase; however, upon binding to guanosine tetraphosphate (ppGpp), the global regulator of stringent response, ObgE exhibits an enhanced interaction with the 50S subunit, resulting in increased equilibrium dissociation of the 70S ribosome into subunits. Furthermore, our cryo-electron microscopy (cryo-EM) structure of the 50S·ObgE·GMPPNP complex indicates that the evolutionarily conserved N-terminal domain (NTD) of ObgE is a tRNA structural mimic, with specific interactions with peptidyl-transferase center, displaying a marked resemblance to Class I release factors. These structural data might define ObgE as a specialized translation factor related to stress responses, and provide a framework towards future elucidation of functional interplay between ObgE and ribosome-associated (p)ppGpp regulators. Together with published data, our results suggest that ObgE might act as a checkpoint in final stages of the 50S subunit assembly under normal growth conditions. And more importantly, ObgE, as a (p)ppGpp effector, might also have a regulatory role in the production of the 50S subunit and its participation in translation under certain stressed conditions. Thus, our findings might have uncovered an under-recognized mechanism of translation control by environmental cues.

SUBMITTER: Feng B

PROVIDER: S-EPMC4028186 | biostudies-literature | 2014 May

REPOSITORIES: biostudies-literature

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Structural and functional insights into the mode of action of a universally conserved Obg GTPase.

Feng Boya B Mandava Chandra Sekhar CS Guo Qiang Q Wang Jie J Cao Wei W Li Ningning N Zhang Yixiao Y Zhang Yanqing Y Wang Zhixin Z Wu Jiawei J Sanyal Suparna S Lei Jianlin J Gao Ning N

PLoS biology 20140520 5

Obg proteins are a family of P-loop GTPases, conserved from bacteria to human. The Obg protein in Escherichia coli (ObgE) has been implicated in many diverse cellular functions, with proposed molecular roles in two global processes, ribosome assembly and stringent response. Here, using pre-steady state fast kinetics we demonstrate that ObgE is an anti-association factor, which prevents ribosomal subunit association and downstream steps in translation by binding to the 50S subunit. ObgE is a ribo ...[more]

PMID: 24844575

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Project description:1,4-Dioxane (1,4-DX) is an environmental contaminant found in drinking water throughout the United States (US). While it is a suspected liver carcinogen, there is no federal or state maximum contaminant level for 1,4-DX in drinking water. Very little is known about the mechanisms by which this chemical elicits liver carcinogenicity. In the present study, we performed chronic and short-term dosing studies in female BDF-1 mice to explore the toxic effects of 1,4-DX. Histopathology studies and a multi-omics approach (transcriptomics and metabolomics) were performed to investigate potential mechanisms of toxicity. Mice were exposed to various concentrations of 1,4-DX (0, 50, 500 and 5,000 mg/L) in their drinking water for one or four weeks. Immunohistochemical analysis of the liver revealed an increase in the number of H2AXγ-positive hepatocytes (a marker of DNA double strand breaks) in mice exposed to 5,000 mg/L 1,4-DX for one and four weeks. In addition, an expansion of precholangiocytes was observed after four weeks of 5,000 mg/L 1,4-DX exposure, as reflected by CK-7 immunostaining. An increase in these markers reflect both DNA damage and repair mechanisms. Liver transcriptomics profiling showed that exposure to 5,000 mg/L 1,4-DX for four weeks resulted in the differential expression of 65 genes compared to controls. Pathway analysis of the transcriptomic data revealed 1,4-DX-induced perturbations in multiple signaling pathways in the liver, including those involved in xenobiotic metabolism, nicotine degradation and glutathione-mediated detoxification. Changes to these pathways as a result of 1,4-DX exposure reflect would be predicted to impact the oxidative stress response, detoxification, and DNA damage. Liver, kidney, stool and urine metabolomics profiling revealed no effect of 5,000 mg/L 1,4-DX exposure for one or four weeks on metabolites. We speculate that this may be reflective of DNA damage being counterbalanced by the repair response, with the net result being a null overall effect on the systemic biochemistry of the exposed mice. Our results show a novel approach for the investigation of environmental chemicals that do not elicit cell death, but have activated the repair systems in response to 1,4-DX exposure

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Structural and functional insights into the mode of action of a universally conserved Obg GTPase.

Publications

Structural and functional insights into the mode of action of a universally conserved Obg GTPase.

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