Mechanistic Insights into the Halophilic Xylosidase Xylo-1 and Its Role in Xylose Production

The Xylo-1 xylosidase, which belongs to the GH43 family, exhibits a high salt tolerance. The present study demonstrated that the catalytic activity of Xylo-1 increased by 195% in the presence of 5 M NaCl. Additionally, the half-life of Xylo-1 increased 25.9-fold in the presence of 1 M NaCl. Through comprehensive analysis including circular dichroism, fluorescence spectroscopy, and molecular dynamics simulations, we elucidated that the presence of Na⁺ ions increased the contact frequency between the surface acidic amino acids and the surrounding water molecules. This resulted in the stabilization of the surrounding hydration layer of Xylo-1. Additionally, Na⁺ ions also stabilized the substrate-binding conformation and the fluctuation of water molecules within the active site, which enhanced the catalytic activity of Xylo-1 by increasing the nucleophilic attack by the water molecules. Ultimately, the optimal reaction conditions for the production of xylose by synergistic catalysis with Xylo-1 and xylanase were determined. The results demonstrated that the conversion yield of the method was high for various sources of xylan, indicating the method could have potential industrial applications. This study explored the structure-activity relationship of catalysis in Xylo-1 under high-salt conditions, provides novel insights into the mechanism of halophilic enzymes, and serves as a reference for the industrial application of Xylo-1.