Rühl, Patrick ; Pöll, Uwe ; Braun, Johannes ; Klingl, Andreas ; Kletzin, Arnulf (2017)
A Sulfur Oxygenase from the Haloalkaliphilic Bacterium Thioalkalivibrio paradoxus with atypically low Reductase Activity.
In: Journal of bacteriology, 199 (4)
doi: 10.1128/JB.00675-16
Artikel, Bibliographie
Kurzbeschreibung (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.
| Typ des Eintrags: | Artikel |
|---|---|
| Erschienen: | 2017 |
| Autor(en): | Rühl, Patrick ; Pöll, Uwe ; Braun, Johannes ; Klingl, Andreas ; Kletzin, Arnulf |
| Art des Eintrags: | Bibliographie |
| Titel: | A Sulfur Oxygenase from the Haloalkaliphilic Bacterium Thioalkalivibrio paradoxus with atypically low Reductase Activity. |
| Sprache: | Englisch |
| Publikationsjahr: | 2017 |
| Titel der Zeitschrift, Zeitung oder Schriftenreihe: | Journal of bacteriology |
| Jahrgang/Volume einer Zeitschrift: | 199 |
| (Heft-)Nummer: | 4 |
| DOI: | 10.1128/JB.00675-16 |
| URL / URN: | https://jb.asm.org/content/199/4/e00675-16.long |
| Kurzbeschreibung (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. |
| ID-Nummer: | pmid:27920296 |
| Fachbereich(e)/-gebiet(e): | 10 Fachbereich Biologie 10 Fachbereich Biologie > Sulfur Biochemistry and Microbial Bioenergetics |
| Hinterlegungsdatum: | 04 Jan 2017 11:03 |
| Letzte Änderung: | 23 Nov 2020 07:24 |
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