Shikimate Pathway and Aromatic Amino Acid Biosynthesis

Abstract The shikimate pathway consists of seven enzymatic reactions whose end product chorismate is the precursor for the synthesis of the aromatic amino acids Phe, Tyr and Trp. In fungi and plants, chorismate is a precursor for many specialised metabolites (i.e. secondary metabolites) that play an important role in the plant's interaction with its environment. The shikimate pathway and aromatic amino acid biosynthesis have been extensively studied in a variety of microorganisms, fungi and plants. Furthermore, the dual involvement of the shikimate and aromatic amino acid biosynthesis pathways in central and specialised metabolism still raises major questions regarding the genes and enzymes involved, and their control, their evolutionary origins and coordinated regulation with genes of associated pathways in response to altered environmental conditions and diverse developmental programs. Key Concepts: The shikimate pathway is the only known pathway for biosynthesis of chorismate and the aromatic amino acids Phe, Tyr and Trp. The shikimate pathway is a bridge between central metabolism and specialised metabolism. The shikimate pathway occurs in various groups of microorganisms, plants and parasites, whereas it does not occur in animals. The pathway enzymes are being targeted for antimicrobial drug and herbicide design. Shikimic acid is an essential metabolite that may balance the metabolic status of the pathway. Chorismate is a branch point metabolite for aromatic amino acids and phenolic compounds. This is an ancient eukaryotic pathway which has been subject to diverse evolutionary processes. Several enzymes from these pathways are allosterically regulated by their end products: Phe, Tyr or Trp. The shikimate pathway and aromatic amino acids, and the specialised metabolites derived from them, simultaneously respond to rhythmic changes.