title: Improvement of Trichoderma reesei xylanase II thermal stability by serine to threonine surface mutations.
abstract: 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.
authors.affiliation: Laboratory of Microorganisms and Biomolecules (LMB), Centre of Biotechnology of Sfax (CBS), University of Sfax, Road of Sidi Mansour Km 6, PO Box 1177, Sfax 3018, Tunisia.
authors.forename: Dorra
authors.initials: D
authors.lastname: Zouari Ayadi
authors.affiliation: Laboratory of Microorganisms and Biomolecules (LMB), Centre of Biotechnology of Sfax (CBS), University of Sfax, Road of Sidi Mansour Km 6, PO Box 1177, Sfax 3018, Tunisia.
authors.forename: Aida
authors.initials: A
authors.lastname: Hmida Sayari
authors.affiliation: Laboratory of Microorganisms and Biomolecules (LMB), Centre of Biotechnology of Sfax (CBS), University of Sfax, Road of Sidi Mansour Km 6, PO Box 1177, Sfax 3018, Tunisia.
authors.forename: Hajer
authors.initials: H
authors.lastname: Ben Hlima
authors.affiliation: Laboratory of Microorganisms and Biomolecules (LMB), Centre of Biotechnology of Sfax (CBS), University of Sfax, Road of Sidi Mansour Km 6, PO Box 1177, Sfax 3018, Tunisia.
authors.forename: Sameh
authors.initials: S
authors.lastname: Ben Mabrouk
authors.affiliation: Laboratory of Microorganisms and Biomolecules (LMB), Centre of Biotechnology of Sfax (CBS), University of Sfax, Road of Sidi Mansour Km 6, PO Box 1177, Sfax 3018, Tunisia.
authors.forename: Monia
authors.initials: M
authors.lastname: Mezghani
authors.affiliation: Laboratory of Microorganisms and Biomolecules (LMB), Centre of Biotechnology of Sfax (CBS), University of Sfax, Road of Sidi Mansour Km 6, PO Box 1177, Sfax 3018, Tunisia. Electronic address: samir.bejar@cbs.rnrt.tn.
authors.forename: Samir
authors.initials: S
authors.lastname: Bejar
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry / Q000235:genetics*; D004795:Enzyme Stability; D004926:Escherichia coli; D007700:Kinetics; D009154:Mutation; D011487:Protein Conformation; D015202:Protein Engineering; D012694:Serine / Q000737:chemistry / Q000235:genetics*; D013696:Temperature; D013912:Threonine / Q000737:chemistry / Q000235:genetics*; D014242:Trichoderma / Q000201:enzymology*
chemical_list: D013912:Threonine; D012694:Serine; D043364:Endo-1,4-beta Xylanases
keywords: Ser/Thr substitutions; Thermostability; Xylanase