# Characterization of Tetrathionate Hydrolase from Acidothermophilic Sulfur-Oxidizing Archaeon Metallosphaera cuprina Ar-4

## TL;DR

This study characterizes a tetrathionate hydrolase enzyme from an acidothermophilic archaeon, revealing its activity and localization.

## Contribution

The first characterization of tetrathionate hydrolase in the genus Metallosphaera.

## Key findings

- TTHMc has a molecular mass of 57 kDa and is active at high temperatures and pH 6.0.
- TTHMc is localized in the cytoplasm, periplasmic space, and membrane with varying activity percentages.
- TTHMc produces thiosulfate, pentathionate, and hexathionate from tetrathionate hydrolysis.

## Abstract

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 TTHMc from the acidothermophilic archaeon Metallosphaera cuprina Ar-4T, 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 TTHMc was determined to be 57 kDa. TTHMc 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 Km and Vmax were 0.35 mmol/L and 86.3 μmol/L, respectively. The presence of 0.01 mol/L Mg2+ enhances the activity of TTHMc, while 0.01 mol/L Ca2+ inhibits its activity. The hydrolysis of tetrathionate (TT) by TTHMc 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.