A newly characterized enzyme from the psilocybin mushroom Psilocybe cubensis, called PcncAAAD, can decarboxylate several aromatic amino acids—including L-tryptophan, L-phenylalanine, and L-tyrosine—as well as chloro-tryptophan derivatives. Unlike previously known aromatic L-amino acid decarboxylases (AAADs) in mammals and plants, this enzyme belongs to a different protein family and contains a unique C-terminal double-β-barrel domain that binds calcium, which is required for its activity and thermal stability. The enzyme likely contributes to psilocybin biosynthesis and offers a new tool for engineering production of aromatic-amino-acid-derived natural products.
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.