Cysteine residues in proteins are subject to diverse redox chemistry. Oxidation of cysteine to S-nitrosocysteine, cysteine sulfenic and sulfinic acids, disulfides and persulfides are a few prominent examples of these oxidative post-translational modifications. In living organisms, these modifications often play key roles in cell signalling and protein function, but a full account of this biochemistry is far from complete. It is therefore an important goal in chemical biology to identify what proteins are subjected to these modifications and understand their physiological function. This review provides an overview of these modifications, how they can be detected and quantified using chemical probes, and how this information provides insight into their role in biology. This survey also highlights future opportunities in the study of cysteine redox chemistry, the challenges that await chemists and biologists in this area of study, and how meeting such challenges might reveal valuable information for biomedical science.

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Gonçalo; et al. (2018): Norbornene Probes for the Detection of Cysteine Sulfenic Acid in Cells. ChemRxiv. Preprint. Norbornene derivatives were validated as probes for cysteine sulfenic acid on proteins and in live cells. Trapping sulfenic acids with norbornene probes is highly selective and revealed a different reactivity profile than the traditional dimedone reagent. The norbornene probe also revealed a superior chemoselectivity when compared to a commonly used dimedone probe. Together, these results advance the study of cysteine oxidation in biological systems. File list (3) download file view on ChemRxiv Manuscript.pdf (3.98 MiB) download file view on ChemRxiv Supporting Information.pdf (5.40 MiB) download file view on ChemRxiv Graphical Abstract.tif (331.55 KiB) Norbornene probes for the detection of cysteine sulfenic acid in cells

Rapid detection of cysteine oxidation in living cells is critical in advancing our understanding of responses to reactive oxygen species (ROS) and oxidative stress. Accordingly, there is a need to develop chemical probes that facilitate proteome‐wide detection of cysteine's many oxidation states. Herein, we report the first whole‐cell proteomics analysis using a norbornene probe to detect the initial product of cysteine oxidation: cysteine sulfenic acid. The oxidised proteins identified in the HeLa cell model represent the first targets of the ROS hydrogen peroxide. The panel of protein hits provides new and important information about the targets of oxidative stress, including 148 new protein members of the sulfenome. These findings provide new leads for the study and understanding of redox signalling and diseases associated with oxidative stress.

Mannich base PIP-199 is the only reported smallmolecule inhibitor of the Fanconi anemia complementation group M-RecQ-mediated genome instability protein (FANCM-RMI), a protein−protein interaction that governs genome instability in the genetic disorders Fanconi anemia and Bloom's syndrome. PIP-199 and analogues with the same indole-derived Mannich base scaffold have been used as tool compounds in diverse biological studies. We report the first published synthesis of PIP-199 and its analogues, demonstrating that PIP-199 immediately decomposes in common aqueous buffers and some organic solvents. Neither PIP-199 nor its more hydrolytically stable analogues show any observable activity in binding and competitive biophysical assays for FANCM-RMI. We conclude that PIP-199 is not an effective tool compound for biological studies and that apparent cellular activity likely arises from the nonspecific toxicity of breakdown products. More generally, apparent inhibitors that share this Mannich scaffold potentially represent a new family of pan-assay interference compounds (PAINS) that should be thoroughly assessed for aqueous stability prior to use in biological studies.