Desulfination by 2'-hydroxybiphenyl-2-sulfinate desulfinase proceeds via electrophilic aromatic substitution by the cysteine-27 proton

A Rhodanese-Like Enzyme that Catalyzes Desulfination of Ergothioneine Sulfinic Acid

Many actinobacterial species contain structural genes for iron-dependent enzymes that consume ergothioneine by way of O2-dependent dioxygenation. The resulting product ergothioneine sulfinic acid is stable under physiological conditions unless cleavage to sulfur dioxide and trimethyl histidine is catalyzed by a dedicated desulfinase. This report documents that two types of ergothioneine sulfinic desulfinases have evolved by convergent evolution. One type is related to metal-dependent decarboxylases while the other belongs to the superfamily of rhodanese-like enzymes. Pairs of ergothioneine dioxygenases (ETDO) and ergothioneine sulfinic acid desulfinase (ETSD) occur in thousands of sequenced actinobacteria, suggesting that oxidative ergothioneine degradation is a common activity in this phylum.

Enzyme-Catalyzed Oxidative Degradation of Ergothioneine

Ergothioneine is a sulfur-containing metabolite that is produced by bacteria and fungi, and is absorbed by plants and animals as a micronutrient. Ergothioneine reacts with harmful oxidants, including singlet oxygen and hydrogen peroxide, and may therefore protect cells against oxidative stress. Herein we describe two enzymes from actinobacteria that cooperate in the specific oxidative degradation of ergothioneine. The first enzyme is an iron-dependent thiol dioxygenase that produces ergothioneine sulfinic acid. A crystal structure of ergothioneine dioxygenase from Thermocatellispora tengchongensis reveals many similarities with cysteine dioxygenases, suggesting that the two enzymes share a common mechanism. The second enzyme is a metal-dependent ergothioneine sulfinic acid desulfinase that produces Nα-trimethylhistidine and SO2 . The discovery that certain actinobacteria contain the enzymatic machinery for O2 -dependent biosynthesis and O2 -dependent degradation of ergothioneine indicates that these organisms may actively manage their ergothioneine content.

The synthesis and oxidation desulfurization performance of Ti-modified hierarchical cheese-like ZSM-5 zeolite

High-performance hierarchical cheese-like C-ZSM-5 nanocrystals are successfully prepared by acid–base treatment and are evaluated for oxidative desulfurization of dibenzothiophene. The acid–base treatment can generate a large number of Si-OH bonds and an open-mesoporous structure, which is conducive for the dispersion of TiO2 and also for the transport of dibenzothiophene and its oxidation products simultaneously. The catalytic results indicate that the hierarchical cheese-like C-ZSM-5 nanocrystals are highly active catalysts for the oxidative desulfurization of dibenzothiophene due to open mesoporosity. Complete conversion was obtained within 80 min at 338 K. The excellent performance is due to the large number of active framework sites and open mesopores generated by post-processing.

Improved Efficiency of the Desulfurization of Oil Sulfur Compounds in Escherichia coli Using a Combination of Desensitization Engineering and DszC Overexpression

The 4S pathway of biodesulfurization, which can specifically desulfurize aromatic S-heterocyclic compounds without destroying their combustion value, is a low-cost and environmentally friendly technology that is complementary to hydrodesulfurization. The four Dsz enzymes convert the model compound dibenzothiophene (DBT) into the sulfur-free compound 2-hydroxybiphenyl (HBP). Of these four enzymes, DszC, the first enzyme in the 4S pathway, is the most severely affected by the feedback inhibition caused by HBP. This study is the first attempt to directly modify DszC to decrease its inhibition by HBP, with the results showing that the modified protein is insensitive to HBP. On the basis of the principle that the final HBP product could show a blue color with Gibbs reagent, a high-throughput screening method for its rapid detection was established. The screening method and the combinatorial mutagenesis generated the mutant AKWC (A101K/W327C) of DszC. After the IC₅₀ was calculated, the feedback inhibition of the AKWC mutant was observed to have been substantially reduced. Interestingly, the substrate inhibition of DszC had also been reduced as a result of directed evolution. Finally, the recombinant BL21(DE3)/BADC*+C* (C* represents AKWC) strain exhibited a specific conversion rate of 214.84 μmol_HBP/g_DCW/h, which was 13.8-fold greater than that of the wild-type strain. Desensitization engineering and the overexpression of the desensitized DszC protein resulted in the elimination of the feedback inhibition bottleneck in the 4S pathway, which is practical and effective progress toward the production of sulfur-free fuel oil. The results of this study demonstrate the utility of desensitization of feedback inhibition regulation in metabolic pathways by protein engineering.