Truncated derivatives of a multidomain thermophilic glycosyl hydrolase family 10 xylanase from Thermotoga maritima reveal structure related activity profiles and substrate hydrolysis patterns

Efficient heteroxylan degradation in the context of economically feasible lignocellulosic biomass biorefining requires xylanolytic enzymes with optimal thermostability and specificity. Therefore, the structure activity relationship of a modular thermophilic glycoside hydrolase family 10 xylanase (xylanase A from Thermotoga maritima MSB8, rXTMA) was investigated through construction of six truncated derivatives, lacking at least one of the 2 N- and/or 2 C-terminal modules. The temperatures for optimal activity and stability of the xylanases were strongly influenced by the presence of the different modules and ranged from 60 to 80 °C and 50 to 80 °C, respectively. In contrast, the pH for optimal activity was only slightly affected (pH 6.0 to 7.0). The tested xylanases retained over 80% activity after 2 h pre-incubation at 50 °C between pH 5.0 and 11.0. Most unexpectedly, changes in the modular structure led to a 26-fold wide range of specific activities of the enzymes towards xylohexaose, while the activity towards insoluble polymeric heteroxylan was comparable for all but one xylanase. rXTMAΔC, lacking the C-terminal modules, had a 60% higher specific activity towards the latter substrate than the wild type enzyme. These results show that key properties of XTMA can be tuned to allow for optimal performance of the enzyme in biotechnological processes such as in the bioconversion of lignocellulosic biomass.