Styrene-oxide isomerase

In enzymology, a styrene-oxide isomerase is an enzyme that catalyzes the chemical reaction


 * styrene oxide $$\rightleftharpoons$$ phenylacetaldehyde

Hence, this enzyme has one substrate, styrene oxide, and one product, phenylacetaldehyde.

This enzyme belongs to the family of isomerases, specifically a class of other intramolecular oxidoreductases. The systematic name of this enzyme class is styrene-oxide isomerase (epoxide-cleaving). This enzyme is also called SOI. This enzyme participates in styrene degradation and is the second step of the pathway after the epoxidation of styrene by styrene monooxygenase.

SOI is an integral membrane protein consisting of four transmembrane helices. Khanppnavar et al. determined the first cryo-EM structures of this protein, which show that SOI forms a novel homo-trimeric assembly, displaying a structural fold reminiscent of ion channels.

The trimeric organization of SOI is essential for its function and is guided by the ferric heme b prosthetic group positioned at the interface of its subunits. This ferric heme b acts as a Lewis acid, interacting with the epoxide oxygen atom to facilitate epoxide ring-opening of substrates.