Cysteine is a building block for many biomolecules that are crucial for living organisms. O-Acetylserine sulfhydrylase (OASS), present in bacteria and plants but absent in mammals, catalyzes the last step of cysteine biosynthesis. This enzyme has been deeply investigated because, beside the biosynthesis of cysteine, it exerts a series of ''moonlighting'' activities in bacteria. We have previously reported a series of molecules capable of inhibiting Salmonella typhimurium (S. typhymurium) OASS isoforms at nanomolar concentrations, using a combination of computational and spectroscopic approaches. The cyclopropane-1,2-dicarboxylic acids presented herein provide further insights into the binding mode of small molecules to OASS enzymes. Saturation transfer difference NMR (STD-NMR) was used to characterize the molecule/ enzyme interactions for both OASS-A and B. Most of the compounds induce a several fold increase in fluorescence emission of the pyridoxal 5 0 -phosphate (PLP) coenzyme upon binding to either OASS-A or OASS-B, making these compounds excellent tools for the development of competition-binding experiments.
Antibacterial adjuvants are of great significance, since they allow the therapeutic dose of conventional antibiotics to be lowered and reduce the insurgence of antibiotic resistance. Herein, we report that an O-acetylserine sulfhydrylase (OASS) inhibitor can be used as a colistin adjuvant to treat infections caused by Gram-positive and Gram-negative pathogens. A compound that binds OASS with a nM dissociation constant was tested as an adjuvant of colistin against six critical pathogens responsible for infections spreading worldwide, Escherichia coli, Salmonella enterica serovar Typhimurium, Klebisiella pneumoniae, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Staphylococcus pseudintermedius. The compound showed promising synergistic or additive activities against all of them. Knockout experiments confirmed the intracellular target engagement supporting the proposed mechanism of action. Moreover, compound toxicity was evaluated by means of its hemolytic activity against sheep defibrinated blood cells, showing a good safety profile. The 3D structure of the compound in complex with OASS was determined at 1.2 Å resolution by macromolecular crystallography, providing for the first time structural insights about the nature of the interaction between the enzyme and this class of competitive inhibitors. Our results provide a robust proof of principle supporting OASS as a potential nonessential antibacterial target to develop a new class of adjuvants and the structural basis for further structure−activity relationship studies.
In ϒ-proteobacteria
and Actinomycetales, cysteine biosynthetic
enzymes are indispensable during persistence and become dispensable
during growth or acute infection. The biosynthetic machinery required
to convert inorganic sulfur into cysteine is absent in mammals; therefore,
it is a suitable drug target. We searched for inhibitors of Salmonella serine acetyltransferase (SAT), the enzyme that
catalyzes the rate-limiting step of l-cysteine biosynthesis.
The virtual screening of three ChemDiv focused libraries containing
91 243 compounds was performed to identify potential SAT inhibitors.
Scaffold similarity and the analysis of the overall physicochemical
properties allowed the selection of 73 compounds that were purchased
and evaluated on the recombinant enzyme. Six compounds displaying
an IC50 <100 μM were identified via an indirect
assay using Ellman’s reagent and then tested on a Gram-negative
model organism, with one of them being able to interfere with bacterial
growth via SAT inhibition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.