Background: Pseudomonas aeruginosa is an opportunistic pathogen problematic
in causing nosocomial infections and is highly susceptible to development of resistance
to multiple antibiotics. The gene encoding methionyl-tRNA synthetase (MetRS)
from P. aeruginosa was cloned and the resulting protein characterized.
Methods: MetRS was kinetically evaluated and the KM
for its three substrates, methionine,
ATP and tRNAMet
were determined to be 35, 515, and 29 μM, respectively. P. aeruginosa
was used to screen two chemical compound libraries containing 1690 individual
Results: A natural product compound (BM01C11) was identified that inhibited the aminoacylation
function. The compound inhibited P. aeruginosa
MetRS with an IC50
μM. The minimum inhibitory concentration (MIC) of BM01C11 was determined against
nine clinically relevant bacterial strains, including efflux pump mutants and hypersensitive
strains of P. aeruginosa
and E. coli.
The MIC against the hypersensitive strain of P. aeruginosa
was 16 μg/ml. However, the compound was not effective against the wild-type and
efflux pump mutant strains, indicating that efflux may not be responsible for the lack of
activity against the wild-type strains. When tested in human cell cultures, the cytotoxicity
) was observed to be 30 μg/ml. The compound did not compete with
methionine or ATP for binding MetRS, indicating that the mechanism of action of the
compound likely occurs outside the active site of aminoacylation.
Conclusion: An inhibitor of P.
aeruginosa MetRS, BM01C11, was identified as a flavonoid
compound named isopomiferin. Isopomiferin inhibited the enzymatic activity of
MetRS and displayed broad spectrum antibacterial activity. These studies indicate that
isopomiferin may be amenable to development as a therapeutic for bacterial infections.