| Summary: | <p>Abstract</p> <p>Background</p> <p>Domain fusion is limited at enzyme one terminus. The issue was explored by swapping a mesophilic <it>Aspergillus niger</it> GH11 xylanase (Xyn) with a hyper-thermophilic <it>Thermotoga maritima</it> glucanase (Glu) to construct two chimeras, Xyn-Glu and Glu-Xyn, with an intention to create thermostable xylanase containing glucanase activity.</p> <p>Results</p> <p>When expressed in <it>E. coli</it> BL21(DE3), the two chimeras exhibited bi-functional activities of xylanase and glucanase. The Xyn-Glu Xyn moiety had optimal reaction temperature (T<sub>opt</sub>) at 50 °C and thermal in-activation half-life (t<sub>1/2</sub>) at 50 °C for 47.6 min, compared to 47 °C and 17.6 min for the Xyn. The Glu-Xyn Xyn moiety had equivalent T<sub>opt</sub> to and shorter t<sub>1/2</sub> (5.2 min) than the Xyn. Both chimera Glu moieties were more thermostable than the Glu, and the three enzyme T<sub>opt</sub> values were higher than 96 °C. The Glu-Xyn Glu moiety optimal pH was 5.8, compared to 3.8 for the Xyn-Glu Glu moiety and the Glu. Both chimera two moieties cooperated with each other in degrading substrates.</p> <p>Conclusions</p> <p>Domain-swapping created different effects on each moiety properties. Fusing the Glu domain at C-terminus increased the xylanase thermostability, but fusing the Glu domain at N-terminus decreased the xylanase thermostability. Fusing the Xyn domain at either terminus increased the glucanase thermostability, and fusing the Xyn domain at C-terminus shifted the glucanase pH property 2 units higher towards alkaline environments. Fusing a domain at C-terminus contributes more to enzyme catalytic activity; whereas, fusing a bigger domain at N-terminus disturbs enzyme substrate binding affinity.</p>
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