Recent Advances in Engineering Ammonia Lyase for Biosynthesis of Aromatic Noncanonical Amino Acids

Aromatic noncanonical amino acids (aromatic ncAAs) are valuable building blocks for pharmaceuticals, agrochemicals, food additives, and specialty chemicals, yet their sustainable and stereoselective synthesis remains challenging. Ammonia-lyases (ALs) have emerged as powerful biocatalysts for the one-step asymmetric hydroamination of arylacrylic acids, and recent advances in protein engineering have substantially enhanced their catalytic performance including efficiency, selectivity, promiscuity, and productivity. This review integrates catalytic mechanisms with the deployment of engineering strategies to illustrate how aromatic amino acid ammonia-lyases (AALs) have evolved into versatile biocatalysts for aromatic ncAAs synthesis. Particular attention is devoted to the engineering of AALs (including phenylalanine, tyrosine, histidine ammonia lyase) and (methyl)aspartate ammonia lyases, highlighting progress in substrate scope expansion, catalytic promiscuity, selectivity modulation, and hybrid catalytic systems. Current limitations and emerging opportunities are further assessed to delineate future directions for next-generation ALs engineering. The engineering strategies and current states of ALs summarized herein provide a conceptual basis for the efficient development of ALs for sustainable aromatic ncAAs biomanufacturing.