TU Darmstadt / ULB / TUbiblio

A Sulfur Oxygenase from the Haloalkaliphilic Bacterium Thioalkalivibrio paradoxus with atypically low Reductase Activity.

Rühl, Patrick and Pöll, Uwe and Braun, Johannes and Klingl, Andreas and Kletzin, Arnulf (2017):
A Sulfur Oxygenase from the Haloalkaliphilic Bacterium Thioalkalivibrio paradoxus with atypically low Reductase Activity.
In: Journal of bacteriology, pp. e00675, 199, (4), ISSN 1098-5530,
[Article]

Abstract

Sequence comparisons showed that the sulfur oxygenase reductase (SOR) of the haloalkaliphilic bacterium Thioalkalivibrio paradoxus Arh 1 (TpSOR) is branching deeply within dendrograms of these proteins (29-34% identity). A synthetic gene encoding the TpSOR expressed in E. coli resulted in a protein of 14.7±0.9 nm in diameter and an apparent molecular mass of 556 kDa. Sulfite and thiosulfate were formed from elemental sulfur in a temperature range of 10-98°C (Topt≈80°C) and a pH range of 6-11.5 (pHopt≈9; 308±78 U/mg protein). Sulfide formation had a maximum specific activity of 0.03 U/mg, or less than 1% of the corresponding activity of other SORs. Hence, reductase activity seems not to be an integral part of the reaction mechanism. The TpSOR was most active at NaCl or glycine betaine concentrations of 0-1 M although 0.2% of the maximal activity was detected even at 5 M NaCl and 4 M betaine. The melting point of the TpSOR was close to 80°C, when monitored by CD spectroscopy or differential scanning fluorimetry, however denaturation kinetics were slow: 55% of the residual activity remained after 25 min incubation at 80°C. Site-directed mutagenesis showed that the active-site residue Cys44 is essential for activity whereas alanine mutants of the two other conserved cysteines retained about 0.5% residual activity. A model of the sulfur metabolism in T. paradoxus is discussed.

IMPORTANCE

Sulfur oxygenase reductases (SORs) are the only enzymes catalyzing an oxygen-dependent disproportionation of elemental sulfur and/or polysulfides to sulfite, thiosulfate and hydrogen sulfide. SORs are known from mesophilic and extremophilic Archaea and Bacteria. All SORs seem to form highly thermostable 24-subunit hollow spheres. They carry a low-potential mononuclear non-heme iron in the active site and an indispensable cysteine, however, their exact reaction mechanisms are unknown. Typically, the reductase activity of SORs is in the range of 5-50% of the oxygenase activity but mutagenesis studies had so far failed to identify residues crucial for the reductase reaction. Here we describe the first SOR, which is almost devoid of the reductase reaction and which comes from a haloalkaliphilic bacterium.

Item Type: Article
Erschienen: 2017
Creators: Rühl, Patrick and Pöll, Uwe and Braun, Johannes and Klingl, Andreas and Kletzin, Arnulf
Title: A Sulfur Oxygenase from the Haloalkaliphilic Bacterium Thioalkalivibrio paradoxus with atypically low Reductase Activity.
Language: English
Abstract:

Sequence comparisons showed that the sulfur oxygenase reductase (SOR) of the haloalkaliphilic bacterium Thioalkalivibrio paradoxus Arh 1 (TpSOR) is branching deeply within dendrograms of these proteins (29-34% identity). A synthetic gene encoding the TpSOR expressed in E. coli resulted in a protein of 14.7±0.9 nm in diameter and an apparent molecular mass of 556 kDa. Sulfite and thiosulfate were formed from elemental sulfur in a temperature range of 10-98°C (Topt≈80°C) and a pH range of 6-11.5 (pHopt≈9; 308±78 U/mg protein). Sulfide formation had a maximum specific activity of 0.03 U/mg, or less than 1% of the corresponding activity of other SORs. Hence, reductase activity seems not to be an integral part of the reaction mechanism. The TpSOR was most active at NaCl or glycine betaine concentrations of 0-1 M although 0.2% of the maximal activity was detected even at 5 M NaCl and 4 M betaine. The melting point of the TpSOR was close to 80°C, when monitored by CD spectroscopy or differential scanning fluorimetry, however denaturation kinetics were slow: 55% of the residual activity remained after 25 min incubation at 80°C. Site-directed mutagenesis showed that the active-site residue Cys44 is essential for activity whereas alanine mutants of the two other conserved cysteines retained about 0.5% residual activity. A model of the sulfur metabolism in T. paradoxus is discussed.

IMPORTANCE

Sulfur oxygenase reductases (SORs) are the only enzymes catalyzing an oxygen-dependent disproportionation of elemental sulfur and/or polysulfides to sulfite, thiosulfate and hydrogen sulfide. SORs are known from mesophilic and extremophilic Archaea and Bacteria. All SORs seem to form highly thermostable 24-subunit hollow spheres. They carry a low-potential mononuclear non-heme iron in the active site and an indispensable cysteine, however, their exact reaction mechanisms are unknown. Typically, the reductase activity of SORs is in the range of 5-50% of the oxygenase activity but mutagenesis studies had so far failed to identify residues crucial for the reductase reaction. Here we describe the first SOR, which is almost devoid of the reductase reaction and which comes from a haloalkaliphilic bacterium.

Journal or Publication Title: Journal of bacteriology
Volume: 199
Number: 4
Divisions: 10 Department of Biology
10 Department of Biology > Sulfur Biochemistry and Microbial Bioenergetics
Date Deposited: 04 Jan 2017 11:03
Identification Number: pmid:27920296
Export:
Suche nach Titel in: TUfind oder in Google

Optionen (nur für Redakteure)

View Item View Item