A Thermostable PL7 Alginate Lyase <i>Vf</i> Aly17 from <i>Vibrio fortis</i> with Broad Substrate Specificity: Structural and Mechanistic Insights into Heat Stability

The low thermostability of alginate lyases has limited their industrial applications. In this study, a strategy based on amino acid multiple sequence alignment, molecular docking, multitemperature molecular dynamics simulations, and site-directed mutagenesis was proposed to elucidate the mechanisms associated with thermostability. In this work, the alginate lyase Vf Aly17 was identified from Vibrio fortis . It exhibits an optimal temperature of 50 °C, retains >50% of its enzymatic activity after incubation at 40–70 °C for 120 min, and maintains >20% activity even at 90 °C. Alanine substitutions at residues Asn94, Lys174, Cys308, and Cys321 resulted in significant reductions in both enzymatic activity and thermostability. Molecular docking and molecular dynamics simulation results revealed a decrease in the number of hydrogen bonds, alterations in the electrostatic interaction network, and a notable decline in the stability of the enzyme–substrate complex. These findings strongly indicate that these residues play crucial roles in mediating thermostability.