Pseudomonas aeruginosa histidyl-tRNA synthetase (HisRS) was selected as a target for antibiotic drug development. The HisRS protein was overexpressed in Escherichia coli and kinetically evaluated. The KM values for interaction of HisRS with its three substrates, histidine, ATP, and tRNAHis, were 37.6, 298.5, and 1.5 μM, while the turnover numbers were 8.32, 16.8, and 0.57 s-1, respectively. A robust screening assay was developed, and 800 natural products and 890 synthetic compounds were screened for inhibition of activity. Fifteen compounds with inhibitory activity were identified, and the minimum inhibitory concentration (MIC) was determined for each against a panel of nine pathogenic bacteria. Each compound exhibited broad-spectrum activity. Based on structural similarity and MIC results, four compounds, BT02C02, BT02D04, BT08E04, and BT09C11, were selected for additional analysis. These compounds inhibited the activity of HisRS with IC50 values of 4.4, 9.7, 14.1, and 11.3 µM, respectively. Time-kill studies indicated a bacteriostatic mode of inhibition for each compound. BT02D04 and BT08E04 were noncompetitive with both histidine and ATP, BT02C02 was competitive with histidine but noncompetitive with ATP, and BT09C11 was uncompetitive with histidine and noncompetitive with ATP. These compounds were not observed to be toxic to human cell cultures.
Keywords: Pseudomonas aeruginosa; antibiotic; drug discovery; histidyl-tRNA synthetase; protein synthesis; tRNA aminoacylation.