The enzyme catalyses the reversible isomerization of 2-(1,2-epoxy-1,2-dihydrophenyl)acetyl-CoA to the unusual unsaturated, oxygen-containing, seven-member heterocyclic enol ether 2-oxepin-2(3H)-ylideneacetyl-CoA, as part of an aerobic phenylacetate degradation pathway.
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The expected taxonomic range for this enzyme is: Bacteria, Archaea
The enzyme catalyses the reversible isomerization of 2-(1,2-epoxy-1,2-dihydrophenyl)acetyl-CoA to the unusual unsaturated, oxygen-containing, seven-member heterocyclic enol ether 2-oxepin-2(3H)-ylideneacetyl-CoA, as part of an aerobic phenylacetate degradation pathway.
enzyme acts as a ring 1,2-epoxyphenylacetyl-CoA isomerase forming oxepin-CoA. It mediates the formation and stabilization of the enolate form by abstracting a proton from the side chain at C2 of ring 1,2-epoxyphenylacetyl-CoA. Addition of the abstracted proton to C8, which becomes C4, of the ring leads to a rearrangement of the double bonds and results in a C-C cleavage of the two epoxy-C-O bonds, yielding the oxepin
enzyme acts as a ring 1,2-epoxyphenylacetyl-CoA isomerase forming oxepin-CoA. It mediates the formation and stabilization of the enolate form by abstracting a proton from the side chain at C2 of ring 1,2-epoxyphenylacetyl-CoA. Addition of the abstracted proton to C8, which becomes C4, of the ring leads to a rearrangement of the double bonds and results in a C-C cleavage of the two epoxy-C-O bonds, yielding the oxepin
mutants with a deletion of paaG gene are unable to grow on phenylacetate as carbon source. Incubation of a paaG mutant with [U-13C8]phenylacetate yields ring-1,2-dihydroxy-1,2-dihydrophenylacetyl lactone. The paaG mutant also converts phenylacetate into ortho-hydroxyphenylacetate, a dead end product of phenylacetate catabolism. The catabolic pathway of phenylacetate involves CoA thioesters. Phenylacetyl-CoA is attacked by a ring-oxygenase/reductase, PaaABCDE proteins, generating a hydroxylated and reduced derivative of phenylacetyl-CoA. The intermediate CoA ester is further metabolized in a complex reaction sequence comprising enoyl-CoA isomerization/hydration, nonoxygenolytic ring opening, and dehydrogenation catalyzed by the PaaG and PaaZ proteins
to 1.85 A resolution. Enzyme consists of three identical subunits related by local three-fold symmetry. The monomer is comprised of a spiral and a helical domain with a fold characteristic of the crotonase superfamily. A putative active site residue, Asp136, is situated in an active site cavity and surrounded by several hydrophobic and hydrophilic residues. The active site cavity is sufficiently large to accommodate a ring substrate. Two conformations are observed for helix H2 located adjacent to the active site. Helix H2 is kinked at Asn81 in two subunits, whereas it is kinked at Leu77 in the other subunit, and the side chain of Tyr80 is closer to Asp136. This indicates that catalytic reaction of PaaG may proceed with large conformational changes at the active site
Grishin, A.M.; Ajamian, E.; Zhang, L.; Rouiller, I.; Bostina, M.; Cygler, M.
Protein-protein interactions in the beta-oxidation part of the phenylacetate utilization pathway: crystal structure of the PaaF-PaaG hydratase-isomerase complex
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Enzyme Nomenclature
5.3.3.18 2-(1,2-epoxy-1,2-dihydrophenyl)acetyl-CoA isomerase
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