Characterisation of wild-type and engineered thermostable cellobiohydrolases from glycosyl hydrolase family 7

Cellulases are important industrial enzymes, which can be used e.g. in the pulp and paper, textile, and detergent industry, as well as for the conversion of cellulosic biomass to ethanol, a transport fuel. Thermostable enzymes are needed in many of these applications. Thermophilic organisms are a potential source for thermostable enzymes for industrial applications. As an alternative, the thermostability of an enzyme can be improved by structure-based rational mutagenesis or directed evolution methods. Here, we present the characterisation of the enzymatic properties of four novel thermostable cellobiohydrolases originating from the thermophililic fungi Acremonium thermophilum, Chaetomium thermophilum, Melanocarpus albomyces and Thermoascus aurantiacus. These GH-7 family enzymes were expressed in the industrially relevant production host Trichoderma reesei, and the kinetics on small soluble substrates, cellobiose inhibition, crystalline cellulose hydrolysis and thermostability of the purified enzymes were determined. Enzymatic properties of these cellobiohydrolases were compared to those of the T.reesei cellobiohydrolase Cel7A, one of the most thoroughly studied fungal cellobiohydrolases. In addition, protein engineering of yeast expressed M. albomyces Cel7B was performed leading to a further improvement of its thermostability. Acknowledgements: This work has been supported by grants from the EU (“Technological improvement for ethanol production from lignocellulose” project; coordinator L. Viikari, VTT), the Academy of Finland (SV) and the Glycoscience Graduate School (SV).