[1S04a] 14. Chemical Biotechnology - Part 2

2:45 PM - 3:00 PM JST(5:45 AM - 6:00 AM UTC)

[1Chemi-09] An energy conserving arginine metabolism found in Archaea

○Yuta Michimori¹, Naoki Ohashi¹, Claudia Szymanski¹, Yuusuke Yokooji¹, Haruyuki Atomi¹ (1. Kyoto Univ. (Japan))

Keywords:

archaea,metabolism,amino acid

It has been demonstrated that ornithine ω-aminotransferase encoded by TK2101 is responsible for proline biosynthesis from ornithine in the hyperthermophilic archaeon Thermococcus kodakarensis. However, the source of ornithine in this organism has remained unclear. Assuming that arginine serves as the precursor of ornithine, we investigated arginine metabolism in T. kodakarensis.Comparative genomic analysis identified a gene of unknown function, TK2200, which co-occurs with carbamate kinase, a member of the arginine deiminase pathway, and exhibits a complementary distribution to arginine deiminase. The TK2200 protein was biochemically characterized and identified as an enzyme which catalyzes the conversion of arginine into citrulline and ammonia while conserving energy via ATP production from ADP and inorganic phosphate. This reaction is reversible and also enables the biosynthesis of arginine from citrulline using free ammonia without requiring aspartate. We designated the enzyme as arginine synthetase.Previously, all forms of life have been presumed to synthesize arginine from citrulline via a two-step pathway involving argininosuccinate synthetase and argininosuccinate lyase, using citrulline, ATP, and aspartate as substrates. Since the identification of arginine deiminase, argininosuccinate synthetase, and argininosuccinate lyase over 50 years ago, these reactions have been considered the only major routes for arginine-citrulline interconversion. The identification of arginine synthetase therefore fundamentally revises our understanding of arginine metabolism.Growth of the TK2200 disruption strain was compared with that of the host strain in synthetic amino acid media. The results indicate that arginine synthetase is required for both proline biosynthesis and contributes to ATP generation. Growth in medium supplemented with citrulline further demonstrated that the enzyme functions in the direction of arginine synthesis in vivo as well. This enzyme is widespread across bacteria and eukaryotes and catalyzes a previously overlooked energy-conserving reaction in microbial amino acid metabolism. Together with ornithine transcarbamoylase and carbamate kinase, this pathway is designated the arginine synthetase pathway.We also describe the metabolic fate of carbamoyl phosphate, an intermediate in this pathway, and demonstrate its physiological importance not only in amino acid metabolism but also in energy conservation and nucleobase biosynthesis.