Understanding Sulfur Based Redox Biology Through Advancements in Chemical Biology
Author | : Thomas Poole |
Publisher | : |
Total Pages | : 154 |
Release | : 2017 |
ISBN-10 | : OCLC:1045425977 |
ISBN-13 | : |
Rating | : 4/5 (77 Downloads) |
Sulfenic acids are fleeting intermediates formed from the oxidation of cysteine thiols by a number of biologically relevant oxidants. Sulfenic acids are quickly converted to other species including disulfides, thiosulfinates, sulfinic acids, or sulfonic acids, leading to changes in protein function. The resulting structural and functional changes can modulate enzyme activity, activate transcription factors, and lead to signaling cascades. Understanding the intricacies of sulfenic acid signaling is important for understanding healthy cellular function and disease states. Identifying the site, timing, and conditions of protein sulfenic acid formation is crucial to understanding cellular redox regulation. The transient nature of sulfenic acids necessitates study with bioorthogonal traps. Current methods for trapping and analyzing sulfenic acids involve the use of dimedone and other nucleophilic 1, 3-dicarbonyl probes that form covalent adducts with cysteinederived protein sulfenic acids. As a mechanistic alternative, we have evaluated highly strained bicyclo[6.1.0]nonyne (BCN) derivatives as concerted traps of sulfenic acids. These strained cycloalkynes react efficiently with sulfenic acids in proteins and small molecules yielding stable alkenyl sulfoxide products at rates more than 100x greater than 1, 3-dicarbonyl reagents enabling kinetic competition with physiological sulfur chemistry. We have demonstrated the selectivity of BCN based probes for sulfenic acids by protein lysate and small molecule experiments. Our experiments show no reactivity with thiols, S-nitrosothiols, sulfinic acids, and sulfonic acids. In contrast, recent literature indicates that BCN and strained alkynes are prone to reacting with thiols under radical conditions via "thiol-yne" reactions, and with persulfides via a mechanism similar to the reaction of alkynes with sulfenic acids. However, it is not completely clear to what extent thiol-yne and persulfide trapping reactions occur under biological conditions. In support of the selectivity of strained alkynes, they are widely used as bioorthogonal reagents in copper free click chemistry. Indeed, the enhanced rates and predictable reactivity of strained alkyne probes make them valuable tools for evaluating transient sulfenic acids in complex cellular environments We have employed computations to identify alternative strained alkynes which should react quickly and more selectively than BCN. Density functionals and hybrid density functionals have been employed with a range of basis sets. We calibrated the computational results with experimental results from three synthesized and two commercially available strained alkynes. The B3LYP-6-31G(2d) theory correlated best with experimental data and was used to assess barrier heights between sulfenic acids and hypothetical alkynes. Computational experiments identified cyclooctynes with endocyclic propargylic heteroatoms as the most viable sulfenic acid traps. Synthesis of a number of choice heterocyclic alkyne candidates was attempted. The enhanced rates demonstrated by current alkynes identify them as new bioorthogonal probes that should facilitate the discovery of previously unknown sulfenic acid sites and their parent proteins. The synthesis and computations described in this work should prove valuable to continued research in this area.