Benzylsuccinate Synthase | |||||||||
---|---|---|---|---|---|---|---|---|---|
Identifiers | |||||||||
EC no. | 4.1.99.11 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
|
The enzyme benzylsuccinate synthase (EC 4.1.99.11) catalyzes the chemical reaction
This enzyme catalyses a radical-type addition of toluene and fumarate as substrates to generate (R)-benzylsuccinate as product, the first step of anaerobic toluene degradation.
Benzylsuccinate synthase is a glycyl-radical enzyme found in many microorganisms such as Thauera aromatica and Aromatoleum tuluolicum responsible for degrading aromatic hydrocarbons, primarily toluene. [1] It operates by catalyzing carbon-carbon bond formation between toluene and fumarate into benzylsuccinate. Benzylsuccinate is then converted to benzoyl CoA in a scheme resembling β-oxidation, and then reductively de-aromatized into metabolites. [2] BSS comprises an α, β, and γ subunit, with the α-subunit containing the activated glycyl-radical, and the β- and γ-subunits being necessary for formation and stability of the cataytically active enzyme. [3] In terms of its catalytic residues, mutagenesis experiments suggest that in addition to Cys493 and Gly829 being critical for catalysis in a T. aromatica T1 strain, mutation of a conserved Arg508 is also critical for benzylsuccinate synthase activity. [4]
This enzyme belongs to the family of glycyl-radical enzymes and is listed under the enzyme commission category of lyases, specifically in the "catch-all" class of carbon-carbon lyases. The systematic name of this enzyme class is benzylsuccinate fumarate-lyase (toluene-forming). This enzyme is also called benzylsuccinate fumarate-lyase, although it does not catalyse t, andhe cleavage of benzylsuccinate. This enzyme participates in feeding toluene into the pathway of benzoate degradation via CoA ligation.
As a result of its intrinsic function, its sequence is being used as a gene marker when studying anoxic toluene contamination sites for active degradation [1]
The mechanism proposed by Heider and coworkers is as follows: activated benzylsuccinate synthase contains a low-reactivity glycine radical at Gly829. [5] Upon binding of both substrates to the active site, the glycine radical generates the thiyl radical on Cys429, which is in close proximity. This thiyl radical abstracts a proton from the methyl group of toluene, which adds to the double bond of fumarate. The benzylsuccinyl radical intermediate then abstracts a proton from Cys429, returning it to the thiyl state which can then restore the glycyl radical resting state.
Aromatic hydrocarbons such as toluene, ethylbenzene, and phenol are persistent pollutants in ecological systems, particularly in groundwater. Moreover, they are difficult to degrade due to their inertness, aromaticity, and lack of easily oxidizable functionalities. Microorganisms such as Magnetospirillum sp. have shown an ability to overcome these chemical obstacles by utilizing radical chemistry to functionalize these hydrocarbons for additional oxidation. [4] However, the industrial utility of benzylsuccinate synthase appears to be limited to anaerobic conditions since the active form of the enzyme is easily and quickly degraded by molecular oxygen. [5] This is present in many ambient environments, and interferes with the radical-glycyl chemistry performed at the active site. It is also believed that the inactive form of benzylsuccinate synthase is not compatible in oxic conditions due to a [4Fe-4S]-cluster that is oxygen sensitive and displays a low midpoint potential. [5]
Salii and coworkers have shown that it is possible to expand the scope of substrates for benzylsuccinate synthase, expanding its applications for the biodegradation of aromatic hydrocarbons. [6] This include m-, p-, and o-cresols which display a hydroxyl group in addition to the methyl group characteristic of toluene. In their work, substrate expansion was accomplished by mutating Ile617 to Val, as Ile617 and Ile620 were two amino acid residues predicted to form a protective hydrophobic wall around the active site.
Tryptophan synthase or tryptophan synthetase is an enzyme that catalyses the final two steps in the biosynthesis of tryptophan. It is commonly found in Eubacteria, Archaebacteria, Protista, Fungi, and Plantae. However, it is absent from Animalia. It is typically found as an α2β2 tetramer. The α subunits catalyze the reversible formation of indole and glyceraldehyde-3-phosphate (G3P) from indole-3-glycerol phosphate (IGP). The β subunits catalyze the irreversible condensation of indole and serine to form tryptophan in a pyridoxal phosphate (PLP) dependent reaction. Each α active site is connected to a β active site by a 25 angstrom long hydrophobic channel contained within the enzyme. This facilitates the diffusion of indole formed at α active sites directly to β active sites in a process known as substrate channeling. The active sites of tryptophan synthase are allosterically coupled.
Cometabolism is defined as the simultaneous degradation of two compounds, in which the degradation of the second compound depends on the presence of the first compound. This is in contrast to simultaneous catabolism, where each substrate is catabolized concomitantly by different enzymes. Cometabolism occurs when an enzyme produced by an organism to catalyze the degradation of its growth-substrate to derive energy and carbon from it is also capable of degrading additional compounds. The fortuitous degradation of these additional compounds does not support the growth of the bacteria, and some of these compounds can even be toxic in certain concentrations to the bacteria.
Methane monooxygenase (MMO) is an enzyme capable of oxidizing the C-H bond in methane as well as other alkanes. Methane monooxygenase belongs to the class of oxidoreductase enzymes.
Desulfatibacillum alkenivorans AK-01 is a specific strain of Desulfatibacillum alkenivorans.
Microbial biodegradation is the use of bioremediation and biotransformation methods to harness the naturally occurring ability of microbial xenobiotic metabolism to degrade, transform or accumulate environmental pollutants, including hydrocarbons, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), heterocyclic compounds, pharmaceutical substances, radionuclides and metals.
In enzymology, a 4-hydroxybenzoyl-CoA reductase (EC 1.3.7.9) is an enzyme found in some bacteria and archaea that catalyzes the chemical reaction
In enzymology, an ethylbenzene hydroxylase (EC 1.17.99.2) is an enzyme that catalyzes the chemical reaction
In enzymology, a succinyl-CoA:(R)-benzylsuccinate CoA-transferase is an enzyme that catalyzes the chemical reaction
The enzyme 4-hydroxyphenylacetate decarboxylase (EC 4.1.1.83) catalyzes the chemical reaction
The enzyme methylisocitrate lyase catalyzes the chemical reaction
The enzyme chorismate synthase catalyzes the chemical reaction
The enzyme cyclohexa-1,5-dienecarbonyl-CoA hydratase (EC 4.2.1.100) catalyzes the chemical reaction
In enzymology, formate C-acetyltransferase is an enzyme. Pyruvate formate lyase is found in Escherichia coli and other organisms. It helps regulate anaerobic glucose metabolism. Using radical non-redox chemistry, it catalyzes the reversible conversion of pyruvate and coenzyme-A into formate and acetyl-CoA. The reaction occurs as follows:
In molecular biology, the citrate synthase family of proteins includes the enzymes citrate synthase EC 2.3.3.1, and the related enzymes 2-methylcitrate synthase EC 2.3.3.5 and ATP citrate lyase EC 2.3.3.8.
Radical SAMenzymes is a superfamily of enzymes that use a [4Fe-4S]+ cluster to reductively cleave S-adenosyl-L-methionine (SAM) to generate a radical, usually a 5′-deoxyadenosyl radical (5'-dAdo), as a critical intermediate. These enzymes utilize this radical intermediate to perform diverse transformations, often to functionalize unactivated C-H bonds. Radical SAM enzymes are involved in cofactor biosynthesis, enzyme activation, peptide modification, post-transcriptional and post-translational modifications, metalloprotein cluster formation, tRNA modification, lipid metabolism, biosynthesis of antibiotics and natural products etc. The vast majority of known radical SAM enzymes belong to the radical SAM superfamily, and have a cysteine-rich motif that matches or resembles CxxxCxxC. Radical SAM enzymes comprise the largest superfamily of metal-containing enzymes.
(R)-benzylsuccinyl-CoA dehydrogenase is an enzyme with systematic name (R)-benzylsuccinyl-CoA:electron transfer flavoprotein oxidoreductase. This enzyme catalyses the following chemical reaction
Thauera aromatica is a species of bacteria. Its type strain is K 172T.
Indoleacetate decarboxylase (IAD) is a glycyl radical enzyme that catalyses the decarboxylation of indoleacetate to form skatole, which is a malodorous organic compound that gives animal faeces their characteristic smell. This decarboxylation is the last step of the tryptophan fermentation in some types of anaerobic bacteria.
Hydrocarbonoclastic bacteria are a heterogeneous group of prokaryotes which can degrade and utilize hydrocarbon compounds as source of carbon and energy. Despite being present in most of environments around the world, several of these specialized bacteria live in the sea and have been isolated from polluted seawater.
Isethionate sulfite-lyase is a glycyl radical enzyme that catalyzes the degradation of isethionate into acetaldehyde and sulfite through the cleavage of a carbon-sulfur bond. This conversion is a necessary step for taurine catabolism in anaerobic bacteria like Bilophila wadsworthia. IslA is activated by the enzyme IslB which uses S-adenoslymethionine (SAM) as the initial radical donor.