Characterization of Tetrathionate Hydrolase from Acidothermophilic Sulfur-Oxidizing Archaeon Metallosphaera cuprina...

Tetrathionate hydrolase (TTH) is a key enzyme for the oxidation of reduced inorganic sulfur compounds (RISCs) with the S₄I pathway, which is distributed in autotrophic or facultative autotrophic sulfur-oxidizing bacteria and archaea. In this study, the enzyme TTH_Mc from the acidothermophilic archaeon Metallosphaera cuprina Ar-4^T, encoded by mcup_1281 and belonging to the pyrroloquinoline quinone (PQQ) family, has been shown to possess tetrathionate hydrolysis activity. The molecular mass of the single subunit of TTH_Mc was determined to be 57 kDa. TTH_Mc is proved to be located in the cytoplasm, periplasmic space, and membrane, and the activity of them accounted for 72.3%, 24.0%, and 3.7% of the total activity. Optimal activity was observed at temperatures above 95 °C and pH 6.0, and the kinetic constants K_m and V_max were 0.35 mmol/L and 86.3 μmol/L, respectively. The presence of 0.01 mol/L Mg²⁺ enhances the activity of TTH_Mc, while 0.01 mol/L Ca²⁺ inhibits its activity. The hydrolysis of tetrathionate (TT) by TTH_Mc results in the production of thiosulfate, pentathionate, and hexathionate. This study represents the first description of TTH in the genus Metallosphaera, providing new theoretical insights into the study of sulfur-oxidizing proteins in acidothermophilic archaea.