pH-Induced structural changes in xylanase GH11 from Thermoanaerobacterium saccharolyticum

Background Glycosyl hydrolase 11 (GH11) xylanase is utilized in various in industrial applications such as baking, fruit juice production, pulp processing, and animal feed. Thermophilic GH11 from Thermoanaerobacterium saccharolyticum (TsaGH11) exhibits maximum activity at acid pH with high catalytic efficiency toward beechwood xylan. TsaGH11 activity is pH dependent, exhibiting relative low hydrolase activity at basic pH. However, the effect of a basic pH environment on the structure of TsaGH11 correlated with enzyme activity remains unknown. To understand pH-dependent activity changes, the crystal structure of TsaGH11 at basic pH was determined and compared with that of TsaGH11 at acid pH. Methods TsaGH11 was crystallized at basic pH of 8.5, and the crystal structure was determined at 1.95 Å resolution. The structure, flexibility, and water molecules of TsaGH11 at pH 8.5 and pH 4.3 were compared. Results The open and closed conformations of TsaGH11 at pH 8.5 are reported. Subtle movements of the side chains of amino acids involved in the substrate-binding cleft and catalytic residues were observed. The overall temperature factor of TsaGH11 at pH 8.5 was higher than that at pH 4.6. The position of water molecules near the catalytic residues in TsaGH11 exhibited variations in different pH environments. Conclusions The structural comparison of TsaGH11 at basic and acidic pH offers valuable insights into the pH-dependent functionality of TsaGH11, enhancing our understanding of these structural alterations.