tailieunhanh - Báo cáo khoa học: The activity of adenylyltransferase in Rhodospirillum rubrum is only affected by a-ketoglutarate and unmodified PII proteins, but not by glutamine, in vitro

Ammonium assimilation is tightly regulated in nitrogen-fixing bacteria; the target of regulation is primarily the activity of the key enzyme glutamine synthetase that is regulated by reversible covalent modification by AMP groups in reactions catalysed by the bifunctional adenylyltransferase (ATase). The properties and regulation of ATase fromEscherichia colihave been studied in great detail. | ỊFEBS Journal The activity of adenylyltransferase in Rhodospirillum rubrum is only affected by a-ketoglutarate and unmodified PII proteins but not by glutamine in vitro Anders Jonsson Pedro F. Teixeira and Stefan Nordlund Department of Biochemistry and Biophysics Stockholm University Sweden Keywords adenylyltransferase ammonium assimilation glutamine synthetase Rhodospirillum rubrum Correspondence S. Nordlund Department of Biochemistry and Biophysics Stockholm University SE-106 91 Stockholm Sweden Fax 46 8157794 Tel 46 8162932 E-mail stefan@ These authors have contributed equally to this work Received 21 November 2006 revised 13 February 2007 accepted 8 March 2007 doi Ammonium assimilation is tightly regulated in nitrogen-fixing bacteria the target of regulation is primarily the activity of the key enzyme glutamine synthetase that is regulated by reversible covalent modification by AMP groups in reactions catalysed by the bifunctional adenylyltransferase ATase . The properties and regulation of ATase from Escherichia coli have been studied in great detail. We have investigated the regulation of ATase from Rhodospirillum rubrum a photosynthetic nitrogen-fixing bacterium. In this diazotroph nitrogenase is regulated at the metabolic level in addition to the transcriptional regulation operating in all diazotrophic bacteria which makes understanding the regulatory features of nitrogen assimilation even more interesting. We show that in R. rubrum in contrast to the E. coli system ATase is primarily regulated by a-ketoglutarate and that glutamine has no effect on neither the adenylylation nor the deadenylylation of glutamine synthetase. Furthermore the role of the regulatory PII proteins is only to stimulate the adenylylation reaction as there is no effect on the reverse reaction. We propose that in R. rubrum and possibly other diazo-trophs a-ketoglutarate plays the central role in the regulation of ATase and thus glutamine .