Computational-Guided Protein Engineering of LaACS Coupled with SAM Synthase Screening Synergistically Boosts ACC Production in <i>E. coli</i>

1-Aminocyclopropane-1-carboxylic acid (ACC) is a nonprotein amino acid commonly found in plants, serving as an ethylene precursor with independent hormone functions that regulate plant growth, development, and stress resistance. Due to its agricultural significance, efforts have focused on boosting its production. In this study, ACC biosynthesis was achieved in <i>E. coli</i> via LaACS (1-aminocyclopropane-1-carboxylate synthase) from <i>Lycoris aurea</i>, which catalyzes <i>S</i>-adenosylmethionine (SAM). To enhance the yield, structural prediction of LaACS using AlphaFold2 and MOE docking identified the mutant LaACS^L243A, which exhibited a doubled <i>V</i>_max (0.018 mM/L/min) and <i>K</i>_cat (12.033 min^-1) and 20% higher <i>K</i>_cat/<i>K</i>_m (15.88 mM^-1 min^{- 1}) than that of the wild type. The intrinsic reasons for the enhanced catalytic efficiency were elucidated through molecular dynamics simulation. Subsequently, through screening of <i>S</i>-adenosylmethionine synthase (SAMS), SAMSa (from <i>Arabidopsis thaliana</i>) was identified as having the highest catalytic activity. Overexpression of the genes encoding SAMSa, MetA (homoserine <i>O</i>-succinyltransferase), and MetH (methionine synthase) successfully increased the ACC yield to 109 mg/L in 50 mL of M9 medium, which is twice that of the unmodified strain. The development of a green, safe, and efficient ACC biosynthetic process is of significant importance for promoting the application of ACC in agricultural science, biology, and medicine.