Publications

• Mycobacterium tuberculosis Is a Natural Ornithine Aminotransferase (rocD) Mutant and Depends on Rv2323c for Growth on Arginine.

  Hampel A., Huber C., Geffers R., Spona-Friedl M., Eisenreich W., Bange F.C.

  Mycobacterium tuberculosis (Mtb) possesses a genetic repertoire for metabolic pathways, which are specific and fit to its intracellular life style. Under in vitro conditions, Mtb is known to use arginine as a nitrogen source, but the metabolic pathways for arginine utilization have not been identi ... >> More

  Mycobacterium tuberculosis (Mtb) possesses a genetic repertoire for metabolic pathways, which are specific and fit to its intracellular life style. Under in vitro conditions, Mtb is known to use arginine as a nitrogen source, but the metabolic pathways for arginine utilization have not been identified. Here we show that, in the presence of arginine, Mtb upregulates a gene cluster which includes an ornithine aminotransferase (rocD) and Rv2323c, a gene of unknown function. Isotopologue analysis by using 13C- or 15N-arginine revealed that in Mtb arginine is not only used as nitrogen source but also as carbon source for the formation of amino acids, in particular of proline. Surprisingly, rocD, which is widespread in other bacteria and is part of the classical arginase pathway turned out to be naturally deleted in Mtb, but not in non-tuberculous mycobacteria. Mtb lacking Rv2323c showed a growth defect on arginine, did not produce proline from arginine, and incorporated less nitrogen derived from arginine in its core nitrogen metabolism. We conclude that the highly induced pathway for arginine utilization in Mtb differs from that of other bacteria including non-tuberculous mycobacteria, probably reflecting a specific metabolic feature of intracellular Mtb. << Less

  PLoS ONE 10:e0136914-e0136914(2015) [PubMed] [EuropePMC]

• Biochemical characterization, homology modeling and docking studies of ornithine delta-aminotransferase--an important enzyme in proline biosynthesis of plants.

  Sekhar P.N., Amrutha R.N., Sangam S., Verma D.P., Kishor P.B.

  Ornithine delta-aminotransferase (OAT) is an important enzyme in proline biosynthetic pathway and is implicated in salt tolerance in higher plants. OAT transaminates ornithine to pyrroline 5-carboxylate, which is further catalyzed to proline by pyrroline 5-carboxylate reductase. The Vigna aconitif ... >> More

  Ornithine delta-aminotransferase (OAT) is an important enzyme in proline biosynthetic pathway and is implicated in salt tolerance in higher plants. OAT transaminates ornithine to pyrroline 5-carboxylate, which is further catalyzed to proline by pyrroline 5-carboxylate reductase. The Vigna aconitifolia OAT cDNA, encoding a polypeptide of 48.1 kDa, was expressed in Escherichia coli and the enzyme was partially characterized following its purification using (NH(4))(2)SO(4) precipitation and gel filtration techniques. Optimal activity of the enzyme was observed at a temperature of 25 degrees C and pH 8.0. The enzyme appeared to be a monomer and exhibited high activity at 4mM ornithine. Proline did not show any apparent effect but isoleucine, valine and serine inhibited the activity when added into the assay mixture along with ornithine. Omission of pyridoxal 5'-phosphate from the reaction mixture reduced the activity of this enzyme by 60%. To further evaluate these biochemical observations, homology modeling of the OAT was performed based on the crystal structure of the ornithine delta-aminotransferase from humans (PDB code 1OAT) by using the software MODELLER6v2. With the aid of the molecular mechanics and dynamics methods, the final model was obtained and assessed subsequently by PROCHECK and VERIFY-3D graph. With this model, a flexible docking study with the substrate and inhibitors was performed and the results indicated that Gly106 and Lys256 in OAT are the important determinant residues in binding as they have strong hydrogen bonding contacts with the substrate and inhibitors. These observations are in conformity with the results obtained from experimental investigations. << Less

  J Mol Graph Model 26:709-719(2007) [PubMed] [EuropePMC]