Unraveling the\nMolecular Determinants of Catalytic\nEfficiency and Substrate Specificity in l‑Amino Acid\nDecarboxylases

l-Tryptophan decarboxylase (TDC) and l-3,4-dihydroxyphenylalanine\ndecarboxylase (DDC) catalyze the decarboxylation of l-tryptophan,\n5-hydroxytryptophan, and l-3,4-dihydroxyphenylalanine. In\nthis study, we analyzed the amino acid compositions of the substrate-binding\npockets of TDC from Catharanthus roseus (<i>Cr</i>TDC) and DDC from Sus scrofa (<i>Ss</i>DDC), explored the specificity of key amino\nacids within these pockets, and elucidated mechanisms influencing\nsubstrate selectivity and catalytic activity in both enzymes, using\nwhole-cell catalysis to screen mutants and determine enzymatic kinetic\nparameters. The results demonstrated that residues Ala-103 and Val-122\nin <i>Cr</i>TDC, along with their corresponding sites Thr-82\nand Ile-101 in <i>Ss</i>DDC, significantly influence substrate\nselectivity and catalytic efficiency. Molecular dynamics simulations\nrevealed that substrate selectivity and catalytic efficiency depends\non the nucleophilic attack distance between the substrate’s\namino group and the C4′ of pyridoxal 5′-phosphate. This\nstudy elucidates the catalytic mechanisms and structural bases of\nTDC and DDC, guiding enhancements in the related aromatic monoamine\nbiosynthesis.