Structure-Based Engineering to Improve Thermostability of Acetivibrio thermocellus AtBgl1A β-Glucosidase

β-Glucosidases are essential enzymes in cellulose degradation and hold significant promise for industrial applications, particularly in biorefinery processes. This study focused on the structural and functional characterization of AtBgl1A, a glycoside hydrolase family 1 β-glucosidase from Acetivibrio thermocellus, and its rational engineering to enhance thermostability. AtBgl1A exhibited over 400-fold higher specificity for laminaribiose than cellobiose, supporting its physiological role in laminaribiose metabolism. The crystal structure of the wild-type AtBgl1A was determined at 2.37-Å resolution, and served as a guide for the design of thermostabilizing mutations. Among variants, the A17S/S39T/T105V triple mutant showed the most significant improvement in thermostability, with a 145 min increase in half-life at 70 and a 5.6 °C elevation in inactivation temperature, while retaining comparable kinetic efficiency. This mutant also outperformed both the wild-type AtBgl1A and commercial enzyme in hydrolyzing cellulose and laminaran at both 60 and 70 °C. Molecular dynamics simulations and residue interaction analyses suggested that the enhanced thermostability was associated with additional hydrogen bonds, van der Waals contacts, and hydrophobic interactions introduced by the mutations. These findings provide valuable insights into the structural determinants of thermostability in GH1 β-glucosidases and demonstrate the potential of rational protein engineering for developing robust biocatalysts for industrial biomass conversion.