The Glycyl Radical Enzyme Arylacetate Decarboxylase from Olsenella scatoligenes

The glycyl radical enzymes (GREs) p-hydroxyphenylacetate (HPA) decarboxylase (HPAD), indoleacetate decarboxylase, and phenylacetate decarboxylase catalyze the radical-mediated decarboxylation of arylacetates, which are products of bacterial aromatic amino acid fermentation. Here, we report the discovery and structural and biochemical investigation of a fourth GRE arylacetate decarboxylase (AAD) from Olsenella scatoligenes that catalyzes HPA decarboxylation. AAD also catalyzes the decarboxylation of p-aminophenylacetate, which is not a substrate of HPAD, and lacks the Fe–S cluster containing small subunit. The structure of AAD in complex with p-hydroxyphenylacetate was determined by X-ray crystallography. The differing substrate ranges and active site structures of AAD and HPAD suggest distinct catalytic mechanisms, underscoring the diversity of radical-mediated decarboxylation reactions.