Simultaneous Screening of Multiple Bacterial tRNA Synthetases Using an Escherichia coli S30-Based Transcription and Translation Assay

A spectrophotometric assay for quantitative measurement of aminoacyl-tRNA synthetase activity

Aminoacyl-tRNA synthetases are enzymes that charge specific tRNAs with their cognate amino acids and play an essential role in the initial steps of protein synthesis. Because these enzymes are attractive targets for drug development in many microorganisms, there is a pressing need for assays suitable for compound screening. We developed (1) a high-throughput assay for measuring aminoacyl-tRNA synthetase activity and (2) an accompanying method for preparing the tRNA substrate. The assay can be performed in 96-well plates and relies on malachite green detection of pyrophosphate (Pi) as an indicator of aminoacyl-tRNA synthetase activity. Analysis of Trypanosoma brucei isoleucyl-tRNA synthetase (IleRS) activity showed that the assay exhibits sensitivity to picomoles of product and yielded a Z' factor of 0.56. We show that this assay is applicable to other aminoacyl-tRNA synthetases and to enzyme inhibition studies. Using this assay, we found that the compound NSC616354 inhibits recombinant IleRS with an IC50 of 0.6 µM. Enzymology studies were also performed with rIleRS and its Km and kcat determined as 3.97 × 10(-5) mol/L and 312 S(-1), respectively. This assay will facilitate the screening of compounds to identify inhibitors of aminoacyl-tRNA synthetases.

Chasing after antibiotic leads

The emergence of drug-resistant pathogens has prompted the search for new antibacterials. In this issue of Chemistry & Biology, Starosta et al. identify specific thiopeptide-antibiotic precursor lead compounds using three complementary high-throughput translation machinery assays.

Initiation of protein synthesis: a target for antimicrobials

BACKGROUND

Translation initiation is a basic and universal biological process that employs significantly different components and displays substantially different mechanisms in bacterial, archaeal and eukaryotic cells. A large amount of detailed mechanistic and structural information on the bacterial translation initiation apparatus has been uncovered in recent years.

OBJECTIVE

to understand which translation initiation steps could represent a novel or underexploited target for the discovery of new and specific antibacterial drugs.

METHODS

Brief descriptions of the properties and mechanism of action of the major antibiotics that have a documented direct inhibitory effect on bacterial translation initiation are presented.

RESULTS/CONCLUSIONS

Considerations and predictions concerning a future scenario for research and identification of bacterial translation initiation inhibitors are presented.