Cyclopropane-1,2-dicarboxylic acids as new tools for the biophysical investigation of O-acetylserine sulfhydrylases by fluorimetric methods and saturation transfer difference (STD) NMR

Abstract

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′-phosphate (PLP) coenzyme upon binding to either OASS-A or OASS-B, making these compounds excellent tools for the development of competition-binding experiments.

Keywords:

• O-Acetylserine sulfhydrylase
• cyclopropane-1,2-dicarboxylic acids
• cysteine biosynthesis
• drug resistance
• saturation transfer difference-NMR

Acknowledgements

The Centro Interdipartimentale Misure “G. Casnati” is kindly acknowledged for the contribution in the analytical determination of the molecules synthesized.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

The work described in this paper was partly carried out under the MSCA-ITN-2014-ETN project INTEGRATE (grant number 642620).