Engineering of phenylalanine ammonia lyase from Rhodotorula graminis for the enhanced synthesis of unnatural L-amino acids

Phenylalanine ammonia lyase (PAL) catalyses the reversible non-oxidative deamination of phenylalanine to trans-cinnamic acid and ammonia. Analogues of L-phenylalanine are incorporated as pharmacophores in several peptidomimetic drug molecules and are therefore of particular interest to the fine chemical industry. PAL from Rhodotorula graminis (RgrPAL) has shown an ability to accept analogues of L-phenylalanine. Our aim was to increase enzymatic activity with directed evolution towards a specific non-natural substrate through the cloning and over-production of PAL in Escherichia coli. The identified variants of RgrPAL with significantly showed more catalytic efficient compared to the wild-type enzyme. These variants were used in a preparative scale biotransformation resulting in a 94% conversion to L-4-Br-phenylalanine (>99% ee).