Oxidation Alters the Architecture of the Phenylalanyl-tRNA Synthetase Editing Domain to Confer Hyperaccuracy

High fidelity during protein synthesis is accomplished by aminoacyl-tRNA synthetases (aaRSs). These enzymes ligate an amino acid to a cognate tRNA and have proofreading and editing capabilities that ensure high fidelity. Phenylalanyl-tRNA synthetase (PheRS) preferentially ligates a phenylalanine to a tRNAPhe over the chemically similar tyrosine, which differs from phenylalanine by a single hydroxyl group. In bacteria that undergo exposure to oxidative stress such as Salmonella enterica serovar Typhimurium, tyrosine isomer levels increase due to phenylalanine oxidation. Several residues are oxidized in PheRS and contribute to hyperactive editing, including against mischarged Tyr-tRNAPhe, despite these oxidized residues not being directly implicated in PheRS activity. Here, we solve a 3.6 Å cryo-electron microscopy structure of oxidized S. Typhimurium PheRS. We find that oxidation results in widespread structural rearrangements in the β-subunit editing domain and enlargement of its editing domain. Oxidization also enlarges the phenylalanyl-adenylate binding pocket but to a lesser extent. Together, these changes likely explain why oxidation leads to hyperaccurate editing and decreased misincorporation of tyrosine. Taken together, these results help increase our understanding of the survival of S. Typhimurium during human infection

QSAR study on the contribution of log P and E(s) to the in vitro antiprotozoal activity of glutathione derivatives.

A series of N-S-blocked glutathione monoester and diester derivatives based on N-benzyloxycarbonyl-S-(2,4-dinitrophenyl)glutathione were evaluated for activity against the pathogenic parasites Trypanosoma brucei brucei, Trypanosoma cruzi, and Leishmania donovani in vitro.Only monoesters 7-9 with a log P value of >2.7 were active inhibitors of T.b. brucei bloodstream form trypomastigotes. Diester compounds 10-15 and 17-27 in most cases were better inhibitors of T.b. brucei than monoester compounds, and some displayed high activity against T. cruzi 14 and L. donovani 17, 19, 29. Compounds 14, 24, and 25 were the most active compounds identified against T.b. brucei having ED(50) values of <0.4 microM. Analysis of the inhibition data (ED(50)) vs calculated log P and E(s) values provided evidence to support membrane penetration and steric factors as the key component in the activity of these compounds. The optimum values for log P and E(s) determined were 5.8 and -0.70, respectively. A QSAR equation relating log(1/ED(50)) vs log P and E(s) was determined and interpreted within the proposed mechanism of activity for these compounds