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Literature summary for 1.8.5.4 extracted from
- Insights into the catalytic mechanism of type VI sulfide quinone oxidoreductases (2021), Biochim. Biophys. Acta, 1862, 148337 .
Cloned(Commentary)
| Cloned (Comment) | Organism |
|---|---|
| gene sqrF, recombinant expression of StrepII-tagged enzyme point mutants in Escherichia coli S17-1 lambda pir cell line and in Thiocapsa roseopersicina cells | Thiocapsa roseopersicina |
Protein Variants
| Protein Variants | Comment | Organism |
|---|---|---|
| C121A | site-directed mutagenesis of gene sqrF, inactive mutant | Thiocapsa roseopersicina |
| C272A | site-directed mutagenesis of gene sqrF, the mutant is more sensitive to iodoacetamide inhibition compared to wild-type. The kcat of the C272A variant slightly decreases, and the affinity of the C272A mutant for duroquinone is lower (increased Km) than those of the wild-type TrSqrF enzyme, but the mutated enzyme has a similar affinity for the sulfide substrate | Thiocapsa roseopersicina |
| C332A | site-directed mutagenesis of gene sqrF, the mutant is much more sensitive to iodoacetamide inhibition compared to wild-type. The kcat and the Vmax values for the C332A variant catalyzed reaction are each one order of magnitude smaller than those data obtained with the wild-type enzyme which coincides with the significantly diminished specific activity measured for this mutant enzyme | Thiocapsa roseopersicina |
| C49A | site-directed mutagenesis of gene sqrF, the C49A enzyme has slightly increased Vmax and kcat values as compared to those of wild-type TrSqrF, but decreased affinity for the sulfide substrate | Thiocapsa roseopersicina |
| additional information | construction of a Thiocapsa roseopersicina fcc, sqrD, and sqrF deletion mutant strain FOQRON from wild-type strain FOQR. Results with the C332A mutant TrSqrF variant are immediately more evident than the C49 and C272 mutations | Thiocapsa roseopersicina |
Inhibitors
| Inhibitors | Comment | Organism | Structure |
|---|---|---|---|
| iodoacetamide | can irreversibly inactivate TrSqrF but only if substrates are present and the enzyme is actively catalyzing its reaction. When the enzyme is inhibited by iodoacetamide, the FAD cofactor is released. The inhibition studies support a mechanism that entails opening and reforming of the heterodisulfide bridge during the catalytic cycle of TrSqrF | Thiocapsa roseopersicina |  |
| additional information | detailed structure-function analysis of the type VI SQR enzyme which enables the proposal of a distinct mechanism of sulfide oxidation for this class. For catalysis of sulfide oxidation, all SQRs require FAD cofactor and a redox-active centre in the active site, usually formed between conserved essential cysteines. SQRs of different types have variation in the number and position of cysteines, highlighting the potential for diverse catalytic mechanisms. The photosynthetic purple sulfur bacterium, Thiocapsa roseopersicina contains a type VI SQR enzyme (TrSqrF) having unusual catalytic parameters and four cysteines likely involved in the catalysis. TrSqrF homology structure modeling, the A chains of three structures of SqrE and SqrA enzymes of Acidianus ambivalens and Aquifex aeolicus, respectively, are selected for model building (PDB IDs 3H8L, 3HYW and 3HYV). The TrSqrF has four cysteines in the primary sequence: Cys332 is ubiquitous, while Cys121 is identified in type I, IV, V and VI SQRs and they correspond to the highly conserved Cys347 and Cys124 of Aquifex aeolicus SQR, respectively. There is no matching residue to the Cys156 of Aquifex aeolicus enzyme in the Thiocapsa roseopersicina and all other type VI SQR proteins. The Cys272 is a unique, characteristic conserved cysteine of the type VI SQRs. Based on the available SQR structures, the corresponding amino acids of this cysteine in type I and type V SQR proteins are localized in a surface loop. The TrSqrF also contains a cysteine residue (Cys49) which is not conserved within any SQR type | Thiocapsa roseopersicina |
KM Value [mM]
| KM Value [mM] | KM Value Maximum [mM] | Substrate | Comment | Organism | Structure |
|---|---|---|---|---|---|
| additional information | - |
additional information | Michaelis-Menten steady-state kinetic study of the mutant versus wild-type enzymes | Thiocapsa roseopersicina | |
| 0.0274 | - |
duroquinone | recombinant wild-type enzyme, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.0275 | - |
duroquinone | recombinant mutant C49A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.0358 | - |
duroquinone | recombinant mutant C332A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.0419 | - |
duroquinone | recombinant mutant C272A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.155 | - |
Na2S | recombinant mutant C332A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.183 | - |
Na2S | recombinant mutant C272A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.209 | - |
Na2S | recombinant wild-type enzyme, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.34 | - |
Na2S | recombinant mutant C49A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
Localization
| Localization | Comment | Organism | GeneOntology No. | Textmining |
|---|---|---|---|---|
| membrane | - |
Thiocapsa roseopersicina | 16020 | - |
Natural Substrates/ Products (Substrates)
| Natural Substrates | Organism | Comment (Nat. Sub.) | Natural Products | Comment (Nat. Pro.) | Rev. | Reac. |
|---|---|---|---|---|---|---|
| n H2S + n quinone | Thiocapsa roseopersicina | - |
polysulfide + n quinol | - |
? | |
Organism
| Organism | UniProt | Comment | Textmining |
|---|---|---|---|
| Thiocapsa roseopersicina | A0A1Z2RRG1 | SqrF | - |
Purification (Commentary)
| Purification (Comment) | Organism |
|---|---|
| recombinant StrepII-tagged enzyme point mutants from Thiocapsa roseopersicina cells by affinity chromatography to homogeneity | Thiocapsa roseopersicina |
Reaction
| Reaction | Comment | Organism | Reaction ID |
|---|---|---|---|
| n HS- + n quinone = polysulfide + n quinol | reaction mechanism, overview | Thiocapsa roseopersicina |
Substrates and Products (Substrate)
| Substrates | Comment Substrates | Organism | Products | Comment (Products) | Rev. | Reac. |
|---|---|---|---|---|---|---|
| additional information | sulfide-dependent duroquinone-reducing activity of purified wild-type and single cysteine mutant TrSqrF variants, overview | Thiocapsa roseopersicina | ? | - |
- |
|
| n H2S + n quinone | - |
Thiocapsa roseopersicina | polysulfide + n quinol | - |
? | |
| Na2S + duroquinone | - |
Thiocapsa roseopersicina | polysulfide + duroquinol + 2 Na+ | - |
? | |
Subunits
| Subunits | Comment | Organism |
|---|---|---|
| ? | x * 44000, recombinant enzyme mutants, SDS-PAGE | Thiocapsa roseopersicina |
Synonyms
| Synonyms | Comment | Organism |
|---|---|---|
| membrane-bound sulfide:quinone oxidoreductases | - |
Thiocapsa roseopersicina |
| SQR | - |
Thiocapsa roseopersicina |
| sqrF | - |
Thiocapsa roseopersicina |
| TrSqrF | - |
Thiocapsa roseopersicina |
| type VI sulfide:quinone oxidoreductase | - |
Thiocapsa roseopersicina |
Temperature Optimum [°C]
| Temperature Optimum [°C] | Temperature Optimum Maximum [°C] | Comment | Organism |
|---|---|---|---|
| 25 | - |
assay at | Thiocapsa roseopersicina |
Turnover Number [1/s]
| Turnover Number Minimum [1/s] | Turnover Number Maximum [1/s] | Substrate | Comment | Organism | Structure |
|---|---|---|---|---|---|
| 0.19 | - |
duroquinone | recombinant mutant C332A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 0.19 | - |
Na2S | recombinant mutant C332A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 1.01 | - |
duroquinone | recombinant mutant C272A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 1.01 | - |
Na2S | recombinant mutant C272A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 1.64 | - |
duroquinone | recombinant wild-type enzyme, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 1.64 | - |
Na2S | recombinant wild-type enzyme, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 2.46 | - |
duroquinone | recombinant mutant C49A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 2.46 | - |
Na2S | recombinant mutant C49A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
pH Optimum
| pH Optimum Minimum | pH Optimum Maximum | Comment | Organism |
|---|---|---|---|
| 8 | - |
assay at | Thiocapsa roseopersicina |
Cofactor
| Cofactor | Comment | Organism | Structure |
|---|---|---|---|
| FAD | required | Thiocapsa roseopersicina | |
IC50 Value
| IC50 Value | IC50 Value Maximum | Comment | Organism | Inhibitor | Structure |
|---|---|---|---|---|---|
| 0.015 | - |
recombinant mutant C332A, pH 8.0, 25°C | Thiocapsa roseopersicina | iodoacetamide | |
| 0.086 | - |
recombinant mutant C272A, pH 8.0, 25°C | Thiocapsa roseopersicina | iodoacetamide | |
| 0.131 | - |
recombinant mutant C49A, pH 8.0, 25°C | Thiocapsa roseopersicina | iodoacetamide | |
| 0.134 | - |
recombinant wild-type enzyme, pH 8.0, 25°C | Thiocapsa roseopersicina | iodoacetamide | |
General Information
| General Information | Comment | Organism |
|---|---|---|
| evolution | SQR proteins are classified into six types (types I-VI, SqrA-F). The photosynthetic purple sulfur bacterium, Thiocapsa roseopersicina contains a type VI SQR enzyme (TrSqrF) having unusual catalytic parameters and four cysteines likely involved in the catalysis. Multiple sequence alignment of selected representative SQR proteins with conserved cysteines in the primary sequence of various sulfide:quinone oxidoreductases (Aquifex aeolicus and Thiocapsa roseopersicina residue numbering) with approximate location of conserved cysteines in relation to the isoalloxazine ring of FAD, based on the structures of various sulfide:quinone oxidoreductases, overview | Thiocapsa roseopersicina |
kcat/KM [mM/s]
| kcat/KM Value [1/mMs-1] | kcat/KM Value Maximum [1/mMs-1] | Substrate | Comment | Organism | Structure |
|---|---|---|---|---|---|
| 1.23 | - |
Na2S | recombinant mutant C332A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 5.31 | - |
duroquinone | recombinant mutant C332A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 5.52 | - |
Na2S | recombinant mutant C272A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 7.24 | - |
Na2S | recombinant mutant C49A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 7.85 | - |
Na2S | recombinant wild-type enzyme, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 24.11 | - |
duroquinone | recombinant mutant C272A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 59.85 | - |
duroquinone | recombinant wild-type enzyme, pH 8.0, 25°C | Thiocapsa roseopersicina | |
| 89.45 | - |
duroquinone | recombinant mutant C49A, pH 8.0, 25°C | Thiocapsa roseopersicina | |
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Release 2023.1 (January 2023)
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