Compounds with capacity to quench the tyrosyl radical in Pseudomonas aeruginosa ribonucleotide reductase

Abstract

Ribonucleotide reductase (RNR) has been extensively probed as a target enzyme in the search for selective antibiotics. Here we report on the mechanism of inhibition of nine compounds, serving as representative examples of three different inhibitor classes previously identified by us to efficiently inhibit RNR. The interaction between the inhibitors and Pseudomonas aeruginosa RNR was elucidated using a combination of electron paramagnetic resonance spectroscopy and thermal shift analysis. All nine inhibitors were found to efficiently quench the tyrosyl radical present in RNR, required for catalysis. Three different mechanisms of radical quenching were identified, and shown to depend on reduction potential of the assay solution and quaternary structure of the protein complex. These results form a good foundation for further development of P. aeruginosa selective antibiotics. Moreover, this study underscores the complex nature of RNR inhibition and the need for detailed spectroscopic studies to unravel the mechanism of RNR inhibitors.

Small Molecule Inhibition of an Exopolysaccharide Modification Enzyme is a Viable Strategy To Block Pseudomonas aeruginosa Pel Biofilm Formation

“…6b and d ). P. aeruginosa contains a class I ribonucleotide reductase, which has been used previously in a HTS to discover P. aeruginosa selective antibiotics that inhibit growth ( 46 , 47 ). Both SK-017154-O and compound 1 had moderate bacteriostatic effects at higher concentrations ( Fig.…”

Inhibitors of the Cancer Target Ribonucleotide Reductase, Past and Present

“…Four of these compounds, namely, NSC36758, NSC45383, NSC361666, and NSC228155, demonstrated antibacterial properties against P.aeruginosa , and both NSC361666 and NSC228155 were shown to deplete dNTP pools, which is consistent with RR inhibition. Both NSC45383 and NSC228155 were found to quench the P.aeruginosa RR2 radical, although these effects could be due to either iron chelation or generation of reactive oxygen species [ 279 ]. A comparison of the high throughput assay hits with reported cytotoxicity data from the NCI-60 panel of cancer cell lines revealed a selection of unique hRR inhibitors with anticancer properties, including NSC73735 [ 280 ].…”