Improvement of Trichoderma reesei xylanase II thermal stability by serine to threonine surface mutations

• Published in: International journal of biological macromolecules 2015-01, Vol.72, p.163-170
• Main Authors: Zouari Ayadi, Dorra, Hmida Sayari, Aida, Ben Hlima, Hajer, Ben Mabrouk, Sameh, Mezghani, Monia, Bejar, Samir
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution - genetics; Endo-1,4-beta Xylanases - chemistry; Endo-1,4-beta Xylanases - genetics; Enzyme Stability; Escherichia coli; Hypocrea jecorina; Kinetics; Mutation; Protein Conformation; Protein Engineering; Serine - chemistry; Serine - genetics; Temperature; Threonine - chemistry; Threonine - genetics; Trichoderma - enzymology
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2014.08.014

Three simple mutants, S80T, S146T, and S149T, and a double mutant, S80T-S149T, were constructed and expressed in Escherichia coli to replace Serine on the surface of the Trichoderma reesei xylanase protein with Threonine residues. While the Wild-type (WT) xylanase showed a half-life time (t1/2) of 20 min at 55 °C, the double mutant was more thermostable exhibiting a t1/2 value of 37 min, followed by the S80T and S149T mutants whose t1/2 values were 25 and 23 min, respectively. At 55 °C, the S146T mutant showed a decrease in thermostability with a t1/2 value of 3 min. While the WT enzyme retained only 32% of residual activity after incubation for 5 min at 60°C, the S80T, S149T, and the S80T-S149T mutant enzymes retained 45%, 41%, and 60%, respectively. Molecular modeling attributed the increase in the thermostability of the S80T and S149T mutants to a new hydrogen bond formation and a packing effect, respectively.