Effect of expression of additional catalytic domain on characteristics of Xylanase Z of Clostridium thermocellum

Abstract

Xylanase Z (XynZ) is a prime part of cellulosome of Clostridium thermocellum. The several domains of the cellulosome complexes are frequently tethered to one another by intrinsically messy regions. This is multidomain xylanase comprising of N-terminus feruloyl esterase followed by substrate binding, dockerin and the catalytic domains. This study design was established to check the expression, activities and other characteristics of different variants of Xylanase Z produced by the C-terminal (XynZ-CB), N-terminal (XynZ-BC) and both terminals (XynZ-BCB) binding domain to catalytic domain in different arrangements. XynZ variants of C. thermocellum with binding domain committed with catalytic domain of C-terminal (XynZ-CB) and N-terminal (XynZ-BC) and both terminals (XynZ-BCB) binding domain and one with catalytic domain at both terminals of the binding domain (XynZ-CBC) were checked in E. coli in different levels like 15, 30, 30, and 33% of cell proteins, respectively. The specific xylanase Z activities of XynZ-CB, XynZ BC, XynZ-BCB and XynZ-BCB were 72, 68, 67 and 200 U mg−1, though their equimolar basis activities were 4176, 3944, 5092 and 19,200 U μM−1 compared to xylan (birchwood). The over-all activities of XynZ-CB, XynZ-BC, XynZ-BCB and XynZ-CBC produced in fermentation culture were 3678, 3579, 3800 and 5400 U L−1 OD600−1, respectively. The results showed that overall yield of XynZ-C remained manifold higher than all other variants due to combined effect of its specific activity and expression level while the activity of variant XynZ-CBC was increased four folds on equimolar basis as compared to its native form. The fruit saccharification increased with the treatment of xylanase and cellulase.