Structural and functional characterization of sulfurtransferase from Frondihabitans sp. PAMC28461.

Sulfurtransferases transfer of sulfur atoms from thiols to acceptors like cyanide. They are categorized as thiosulfate sulfurtransferases (TSTs) and 3-mercaptopyruvate sulfurtransferases (MSTs). TSTs transfer sulfur from thiosulfate to cyanide, producing thiocyanate. MSTs transfer sulfur from 3-mercaptopyruvate to cyanide, yielding pyruvate and thiocyanate. The present study aimed to isolate and characterize the sulfurtransferase FrST from Frondihabitans sp. PAMC28461 using biochemical and structural analyses. FrST exists as a dimer and can be classified as a TST rather than an MST according to sequence-based clustering and enzyme activity. Furthermore, the discovery of activity over a wide temperature range and the broad substrate specificity exhibited by FrST suggest promising prospects for its utilization in industrial applications, such as the detoxification of cyanide.

Structural basis for the substrate specificity of an S-formylglutathione hydrolase derived from Variovorax sp. PAMC 28711.

S-Formylglutathione hydrolase was originally known to catalyze the hydrolysis of S-formylglutathione to formate and glutathione. However, this enzyme has a broader esterase activity toward substrates containing thioester and ester bonds. In a previous study, we identified a new S-formylglutathione hydrolase (VaSFGH) gene in the Antarctic bacterium Variovorax sp. PAMC 28711, and recombinant VaSFGH protein was purified and characterized. Previous enzyme activity assays showed that VaSFGH has high activity, especially toward short-chain p-nitrophenyl esters (C2-C4). In this study, we determined the crystal structure of substrate-free VaSFGH at a resolution of 2.38 Å. In addition, p-nitrophenyl ester-bound VaSFGH structure models were generated by molecular docking simulations to obtain structural evidence of its substrate specificity. Comparative structural analysis of the apo-form and p-nitrophenyl ester-bound VaSFGH model structures revealed that large substrates could not bind inside the hydrophobic substrate-binding pocket because of the intrinsically static and relatively small substrate-binding pocket size of VaSFGH. This study provides useful information for further protein engineering of SFGHs for industrial use.