Figure 3.

Comparison of different pathways for the production of amino acid monomers from chorismate. Chorismic acid is converted to prephenic acid (upper pathway) by the action of chorismate mutases (e.g: AroQ, PheA, TyrA). The canonical aromatic decarboxylation produces aromatic amino acids (prephenate dehydratase (Pht) for Phe and prephenate dehydrogenase (Phd) for Tyr). An unusual nonaromatic decarboxylation of prephenate is catalyzed by a group of prephenate decarboxylases (PDXs) which include BacA (anticapsin in bacilysin), SalX (tetrahydro-phenylalanine (H₄Phe) in salinisporamide) and AerD (Choi in aeruginoside 126A). In secondary metabolism, chorismic acid is converted to 8 by a 4-amino-4-deoxychorismate synthase (such as CmlB (chloramphenicol) and SvnN (stravidin)). Similar to the upper pathway, 8 rearranges to 9 by the action of a mutase (CmlD (chloramphenicol) and SvnK (stravidin)). In chloramphenicol biosynthesis, a typical aromatic decarboxylation is catalyzed by CmlC, followed by an aminotransferase to give the monomer p-amino phenyl alanine. However, for Acm (4), a unique nonaromatic decarboxylation retains the 1,4 cyclohexadiene functionality as in the prephenate skeletal structure, and we propose a novel PDX is catalyzing this step. Unusual nonaromatic decarboxylation pathways are highlighted.