Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6491673 | Journal of Biotechnology | 2013 | 27 Pages |
Abstract
Xylanase Z of Clostridium thermocellum exists as a complex in the cellulosome with N-terminus feruloyl esterase, a carbohydrate binding module (CBM6) and a dockerin domain. To study the role of the binding modules on the activity of XynZ, different variants with the CBM6 attached to the catalytic domain at its C-terminal (XynZ-CB) and N-terminal (XynZ-BC), and the CBM22 attached at N-terminus (XynZ-Bâ²C) were expressed in Escherichia coli at levels around 30% of the total cell proteins. The activities of XynZ-BC, XynZ-CB and XynZ-Bâ²C were 4200, 4180 and 20,700 U μMâ1 against birchwood xylan, respectively. Substrate binding studies showed that in case of XynZ-BC and XynZ-CB the substrate birchwood xylan remaining unbound were 51 and 52%, respectively, whereas in the case of XynZ-Bâ²C the substrate remaining unbound was 39% under the assay conditions used. The molecular docking studies showed that the binding site of CBM22 in XynZ-Bâ²C is more exposed and thus available for substrate binding as compared to the tunnel shape binding pocket produced in XynZ-BC and thus hindering the substrate binding. The substrate binding data for the two constructs are in agreement with this explanation.
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Authors
Muhammad Imran M. Khan, Muhammad Sajjad, Saima Sadaf, Rehan Zafar, Umer H.K. Niazi, Muhammad Waheed Akhtar,