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영어

The applications of enzymes industrial processes are often hampered by their instability at high temperature. The selection and optimization of unstable residues are critical in improving the thermostability of enzymes by protein engineering. In this study, computational modeling was used to optimize unstable regions of Bacillus subtilis xylanase (Bcx) instead of random mutagenesis. The thermal fluctuations of unstable region known as important to the thermal
unfolding of Bcx were investigated by the Molecular dynamics simulations at 300K and 330K to identify unstable residues. The N52 site showed the highest thermal fluctuations. Subsequently, computational design was conducted to predict the optimal sequences of unstable residues. Five optimal single mutants were predicted by the computational design, the N52Y mutation showed the thermostabilization effect. The N52 residue is conserved in Bacillus species xylanases and the structure analysis revealed that the N52Y mutation introduced more hydrophobic clusters for the thermostability, and a more favorable aromatic stacking environment for substrate binding. The quadruple mutant (F48Y/T50V/N52Y/T147L) was constructed by the introduction of the N52Y mutation into the thermostable triple (F48Y/T50V/T147L) designed in our previous study. The
quadruple mutant improved thermal properties with the synergistic effects due to the N52Y mutation. In this study, we confirm that flexible residues at high temperature can be promising targets to improve the thermostability of enzymes.