A fungal enzyme called PcncAAAD, which decarboxylates aromatic amino acids, is activated by calcium through two metal-binding sites. The primary activation site (site A) lies between the N-terminal domain and a unique C-terminal appendage; binding calcium there stabilizes a 'lid-rim' structure that preserves the substrate-binding pocket. A secondary site (site B) within the C-terminal domain helps stabilize the enzyme's overall structure. Computer simulations and lab tests show that disrupting site A or the lid-rim severely distorts the active site and reduces or eliminates activity. Sodium does not activate the enzyme. The work clarifies how calcium activates this enzyme and may guide engineering of similar enzymes for making aromatic amino acid derivatives.
An enzyme called PcncAAAD, a noncanonical aromatic L-amino acid decarboxylase, is activated by calcium through a specific mechanism. Using computer simulations and lab experiments, researchers identified two calcium-binding sites: site A, at the junction of two enzyme domains, primarily drives activation, while site B within a unique tail domain stabilizes the enzyme's structure. Calcium binding at site A stabilizes a 'lid-rim' structure that maintains the substrate-binding pocket. Mutations disrupting site A or this lid-rim severely distort the active site and reduce or eliminate enzyme activity. These findings clarify how calcium activates this enzyme and may aid in designing enzymes to produce aromatic amino acid derivatives.