Reaction mechanism of tetrathionate hydrolysis based on the crystal structure of tetrathionate hydrolase from Acidithiobacillus ferrooxidans

Abstract

Tetrathionate hydrolase (4THase) plays an important role in dissimilatory sulfur oxidation in the acidophilic iron-and sulfur-oxidizing bacterium Acidithiobacillus ferrooxidans. The structure of recombinant 4THase from A. ferrooxidans (Af-Tth) was determined by X-ray crystallography to a resolution of 1.95 Å. Af-Tth is a homodimer, and its monomer structure exhibits an eight-bladed β-propeller motif. Two insertion loops participate in dimerization, and one loop forms a cavity with the β-propeller region. We observed unexplained electron densities in this cavity of the substrate-soaked structure. The anomalous difference map generated using diffraction data collected at a wavelength of 1.9 Å indicated the presence of polymerized sulfur atoms. Asp325, a highly conserved residue among 4THases, was located near the polymerized sulfur atoms. 4THase activity was completely abolished in the sitespecific Af-Tth D325N variant, suggesting that Asp325 plays a crucial role in the first step of tetrathionate hydrolysis. Considering that the Af-Tth reaction occurs only under acidic pH, Asp325 acts as an acid for the tetrathionate hydrolysis reaction. The polymerized sulfur atoms in the active site cavity may represent the intermediate product in the subsequent step.

Tetrathionate hydrolase from the acidophilic microorganisms

“…Recombinant Af -Tth crystals (hexagonal cylinder with dimensions of 0.2 mm × 0.05 mm × 0.05 mm) have been successfully obtained ( Kanao et al, 2013 ) and the X-ray crystallographic results reported ( Kanao et al, 2021 ). Af -Tth is a homodimer and its monomer structure exhibits an eight-bladed beta-propeller motif, as determined by X-ray crystallography at 1.95 Å resolution.…”

“…These results suggest that the sole cysteine residue (Cys301) in Af-Tth is not involved in the tetrathionate hydrolysis reaction or subunit assembly, indicating a novel cysteine-independent reaction mechanism for this enzyme. obtained (Kanao et al, 2013) and the X-ray crystallographic results reported (Kanao et al, 2021). Af-Tth is a homodimer and its monomer structure exhibits an eight-bladed beta-propeller motif, as determined by X-ray crystallography at 1.95 Å resolution.…”

Chemical evolution of primordial salts and organic sulfur molecules in the asteroid 162173 Ryugu

“…2 33 , and then a hydrolysis reaction (Eq. 3 shows that for tetrathionate, but the reactions for other S n O 6 2− are analogous) produces S 8 as the most stable end product 34 (S 8 detection by Aponte et al 2023 14 ) [Eq. 3 ]: …”

The Complex Interplay of Sulfur and Arsenic Bioenergetic Metabolisms in the Arsenic Geochemical Cycle

“…This latter enzyme, typical of acidophiles, is a homodimer whose final products and localization (periplasmic or bound to the outer membrane) are still under debate. The structure resolution of the enzyme from Acidithiobacillus ferrooxidans allowed to propose a mechanism for S 0 , S2O3 2and SO4 2generation from the hydrolysis of S4O6 2- (Kanao et al 2021). In phototrophic bacteria, instead, the soluble periplasmic cytochrome c thiosulfate dehydrogenase TsdA catalyses the S2O3 2oxidation to S4O6 2-, transferring electrons either to a dedicated cytochrome c TsdB, encoded upstream, or to a unspecific cytochrome or an HiPIP (see Kurth et al 2016).…”