Capturing a Sulfenic Acid with Arylboronic Acids and Benzoxaborole

Abstract

Post-translational redox generation of cysteine-sulfenic acids (Cys-SOH) functions as an important reversible regulatory mechanism for many biological functions, such as signal transduction, balancing cellular redox states, catalysis, and gene transcription. Herein we show that arylboronic acids and cyclic benzoxaboroles can form adducts with sulfenic acids in aqueous medium and that these boron-based compounds can potentially be used to trap biologically significant sulfenic acids. As proof of principle we demonstrate that a benzoxaborole can inhibit the enzyme activity of an iron-containing nitrile hydratase, which requires a catalytic αCys114-SOH in the active site. The nature of the adduct and the effect of the boronic acid's pK(a)(B) on the stability constant of the adduct are discussed within.

Recent Developments in the Chemistry and Biological Applications of Benzoxaboroles

“…30 Recently, benzoxaborole 1, along with arylboronic acids, was shown to form adducts with sulfenic acids in aqueous solution (Scheme 5). 47 The techniques used for the investigation of the adduct formation (and the equilibria involved) included UV/vis spectrophotometry, isothermal titration calorimetry (ITC), electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and 11 B NMR.…”

“…Importantly, the iron-based NHases require cysteine-derived sulfenic acid at its active site to retain the catalytic activity. 22,47 In an enzymatic assay conducted with photoactivated R. erythropolis NHase, benzoxaborole showed a superior capacity for inhibition compared to investigated arylboronic acids. These findings provide an exciting opportunity for new applications of benzoxaboroles, based on the interactions with sulfenic acidbearing biological targets.…”

Mass spectrometry in studies of protein thiol chemistry and signaling: Opportunities and caveats

“…The finding of IAM reactivity with Cys-SOH opens a possible avenue to address this question and an approach is described in Figure 5. These challenges have prompted investigations of other reactive partners for Cys-SOH such as aryl boronic acid substrates [178] and the recently reported strained bicyclononynes, which covalently trap Cys-SOH by mechanisms distinct from the 1,3-dicarbonyls [40]. The latter has revealed reaction rates with protein Cys-SOH >300 times faster than dimedone allowing for effective trapping of Cys-SOH using micromolar amounts of probe and much shorter incubation times.…”

Chemoselective ratiometric imaging of protein S-sulfenylation

“…When added to proteins, the nucleophilic α-carbon reacts with S -sulfenylated thiols to form a stable thioether, covalently bridging the probe to the site of S -sulfenylation. This covalent adduct can then be detected either by anti-dimedone antibodies 10 or by conjugation to a reporter group 4, 5, 7, 8, 11 . Strained cyclooctynes, benzoxaborazoles, and boronic acids have also been explored as sulfenic acid labeling reagents 11, 12 .…”

“…This covalent adduct can then be detected either by anti-dimedone antibodies 10 or by conjugation to a reporter group 4, 5, 7, 8, 11 . Strained cyclooctynes, benzoxaborazoles, and boronic acids have also been explored as sulfenic acid labeling reagents 11, 12 . Despite this expanded toolset, each approach relies on tethered fluorophores or secondary conjugation to a reporter group 13, 14 , which complicate imaging S -sulfenylation in living cells by increasing background or requiring excessive washing.…”