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  • 1.
    Berthold, Catrine L.
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Wang, He
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Högbom, Martin
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Mechanism of ADP-ribosylation removal revealed by the structure and ligand complexes of the dimanganese mono-ADP-ribosylhydrolase DraG2009In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, no 34, p. 14247-14252Article in journal (Refereed)
    Abstract [en]

    ADP-ribosylation is a ubiquitous regulatory posttranslational modification involved in numerous key processes such as DNA repair, transcription, cell differentiation, apoptosis, and the pathogenic mechanism of certain bacterial toxins. Despite the importance of this reversible process, very little is known about the structure and mechanism of the hydrolases that catalyze removal of the ADP-ribose moiety. In the phototrophic bacterium Rhodospirillum rubrum, dinitrogenase reductase-activating glycohydrolase (DraG), a dimanganese enzyme that reversibly associates with the cell membrane, is a key player in the regulation of nitrogenase activity. DraG has long served as a model protein for ADP-ribosylhydrolases. Here, we present the crystal structure of DraG in the holo and ADP-ribose bound forms. We also present the structure of a reaction intermediate analogue and propose a detailed catalytic mechanism for protein de-ADP-ribosylation involving ring opening of the substrate ribose. In addition, the particular manganese coordination in DraG suggests a rationale for the enzyme's preference for manganese over magnesium, although not requiring a redox active metal for the reaction.

  • 2.
    Teixeira, Pedro
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Wang, He
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Stefan, Nordlund
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nitrogenase switch-off and regulation of ammonium assimilation in response to light deprivation in Rhodospirillum rubrum are influnced by the nitrogen source used during growth2010In: Journal of Bacteriology, ISSN 0021-9193, E-ISSN 1098-5530, Vol. 192, no 5, p. 1463-1466Article in journal (Refereed)
    Abstract [en]

    Nitrogen fixation and ammonium assimilation in Rhodospirillum rubrum are regulated in response to changes in light availability, and we show that the response in terms of glutamine synthetase activity and PII modification is dependent on the nitrogen source used for growth, N2 or glutamate, although both lead to nitrogenase derepression.

  • 3.
    Wang, He
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Metabolic regulation of nitrogen fixation in Rhodospirillum rubrum2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nitrogen, along with carbon, hydrogen and oxygen, is amongst the most abundant elements in all living cells. The capability to convert atmospheric dinitrogen to biologically usable nitrogen compounds is only found in some prokaryotes. Biological nitrogen fixation, the reduction of dinitrogen to ammonia, is the entry step into the global nitrogen cycle. Nitrogenase, the enzyme responsible for dinitrogen reduction, requires large amounts of ATP and reducing equivalents. Consequently, the nitrogen fixation process is subjected to sophisticated regulatory networks that respond to multiple environmental stimuli. In the free-living photosynthetic nitrogen-fixing bacterium Rhodospirillum rubrum, the activity of nitrogenase is tightly regulated at the post-translational level by reversible ADP-ribosylation in response to cellular changes in nitrogen and energy status, the so-called “switch-off” effect. Our studies have been focused on identifying the intracellular signal(s) and protein components acting during “switch-off”, and elucidating the mechanism underlying this regulation. We have shown that PII signal transduction proteins and the ammonium transporter AmtB1 play central roles in the signal transduction pathway leading to the post-translational regulation of nitrogenase, in particular, the involvement of AmtB1-PII complex formation during ammonium “switch-off”. In contrast, a different signaling pathway is operating during the energy “switch-off”, and several interesting differences are highlighted here. In addition, we have solved a high-resolution structure of Dinitrogenase Reductase Activating Glycohydrolase (DRAG) using X-ray crystallography. A detailed mechanism of ADP-ribose removal by DRAG is proposed, with our structural and functional studies on DRAG supporting a reversible membrane association mechanism of regulating its activity, further controlling the activity of nitrogenase.

  • 4.
    Wang, He
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Franke, Claudia C.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Reversible membrane association of dinitrogenase reductase activating glycohydrolase in the regulation of nitrogenase activity in Rhodospirillum rubrum; dependence on GlnJ and AmtB12005In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 253, no 2, p. 273-279Article in journal (Refereed)
    Abstract [en]

    In the photosynthetic bacterium Rhodospirillum rubrum nitrogenase activity is regulated by reversible ADP-ribosylation of dinitrogenase reductase in response to external so called “switch-off” effectors. Activation of the modified, inactive form is catalyzed by dinitrogenase reductase activating glycohydrolase (DRAG) which removes the ADP-ribose moiety. This study addresses the signal transduction between external effectors and DRAG. R. rubrum, wild-type and PII mutant strains, were studied with respect to DRAG localization. We conclude that GlnJ clearly has an effect on the association of DRAG to the membrane in agreement with the effect on regulation of nitrogenase activity. Furthermore, we have generated a R. rubrum mutant lacking the putative ammonium transporter AmtB1 which was shown not to respond to “switch-off” effectors; no loss of nitrogenase activity and no ADP-ribosylation. Interestingly, DRAG was mainly localized to the cytosol in this mutant. Overall the results support our model in which association to the membrane is part of the mechanism regulating DRAG activity.

  • 5.
    Wang, He
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Teixeira, Pedro
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Jonsson, Anders
    Vintila, Simina
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Transcription of the PII-AmtB encoding operons in Rhodospirillum rubrum and studies of the functional role(s) of GlnB, GlnJ and AmtB1 in nitrogen metabolismArticle in journal (Refereed)
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