Development and validation of a whole-cell inhibition assay for bacterial methionine aminopeptidase by surface-enhanced laser desorption ionization-time of flight mass spectrometry

New Urea Derivatives as Potential Antimicrobial Agents: Synthesis, Biological Evaluation, and Molecular Docking Studies

A series of new urea derivatives, containing aryl moieties as potential antimicrobial agents, were designed, synthesized, and characterized by ¹H NMR, ¹³C NMR, FT-IR, and LCMS spectral techniques. All newly synthesized compounds were screened in vitro against five bacterial strains (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Staphylococcus aureus) and two fungal strains (Candida albicans and Cryptococcus neoformans). Variable levels of interaction were observed for these urea derivatives. However, and of major importance, many of these molecules exhibited promising growth inhibition against Acinetobacter baumannii. In particular, to our delight, the adamantyl urea adduct 3l demonstrated outstanding growth inhibition (94.5%) towards Acinetobacter baumannii. In light of this discovery, molecular docking studies were performed in order to elucidate the binding interaction mechanisms of the most active compounds, as reported herein.

Growth inhibition of Escherichia coli and methicillin-resistant Staphylococcus aureus by targeting cellular methionine aminopeptidase

Methionine aminopeptidase (MetAP) catalyzes the N-terminal methionine excision from the majority of newly synthesized proteins, which is an essential cotranslational process required for cell survival. As such, MetAP has become an appealing target for the development of antimicrobial therapeutics with novel mechanisms of action. By screening a library of small organic molecules, we previously discovered a class of compounds that selectively inhibit the Fe(II)-form of MetAP. Herein, we demonstrate that some of these compounds and their newly synthesized derivatives halt the growth of Escherichia coli and Staphylococcus aureus cells with significant potency. The most potent compound inhibited methicillin-resistant S. aureus (MRSA) growth with an IC(50) value of 1 μM and MIC of 0.7 μg/ml. Two cell-based assays were used to verify that MetAP is the intracellular target in E. coli cells. These findings can serve as foundation for the development of novel therapeutics against an ever increasing threat by drug resistant staphylococcal infections.

A high-throughput absorbance-based assay for methionine produced by methionine aminopeptidase using S-adenosyl-L-methionine synthetase

Methionine aminopeptidase (MAP) (E.C. 3.4.11.18) is a metallopeptidase that cleaves the N-terminal methionine (Met) residue from some proteins. MAP is essential for growth of several bacterial pathogens, making it a target for antibacterial drug discovery. MAP enzymes are also present in eukaryotic cells, and one is a target for antiangiogenic cancer therapy. To screen large compound libraries for MAP inhibitors as the starting point for drug discovery, a high-throughput-compatible assay is valuable. Here the authors describe a novel assay, which detects the Met product of MAP-catalyzed peptide cleavage by coupling it to adenosine triphosphate (ATP)-dependent production of S-adenosyl-L-methionine (SAM) and inorganic phosphate (P(i)) by SAM synthetase (MetK) combined with inorganic pyrophosphatase. The three P(i) ions produced for each Met consumed are detected using Malachite Green/molybdate reagent. This assay can use any unmodified peptide MAP substrate with an N-terminal Met. The assay was used to measure kinetic constants for Escherichia coli MAP using Mn(2+) as the activator and the peptide Met-Gly-Met-Met as the substrate, as well as to measure the potency of a MAP inhibitor. A Mn(2+) buffer is described that can be used to prevent free Mn(2+) depletion by chelating compounds from interfering in screens for MAP inhibitors.

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.