Recent View on Heterologous Expression of Thermostable Fungal Cellulases, Focused on Expression Factory of Pichia Pastoris

Thermophilic fungal cellulases are promising enzymes play remarkable functional role in the industrial production of biofuel, detergent and textile, pulp and paper. Fungi are the most robust specie among all organisms having the ability of cellulases production, while most of them cannot tolerate to high temperature. A kind of newly discovered fungi, thermophilic fungi are the only well studied eukaryotes that can tolerate and stably cultivate at temperatures over 45°C. On behalf of these characteristics thermophilic fungi have been received mounting interest and their thermostable enzymes are much warranted. In the recent years, thermophilic cellulases have significant development in many features, such as components purification and characterization of the cellulases, perception of the degradation mode of cellulose, cloning and expression of cellulase genes, finding out the designs and shapes of cellulase components, enhancing the characteristics of cellulases through fusion and mutation processes , considering associations in the structure and function of cellulases and showing the industrial potential of cellulases. Pichia pastoris a methylotrophic yeast is an extensively exploited expression system for the heterologous enzymes production. With numerous beneficial characteristics such as growth to high cell density and high competence for enzymes secretion has emerged P. pastoris a promising expression host, besides P. pastoris provides a strong, methanol inducible promoter of the alcohol oxidase 1 (AOX1) gene used in the expression host to enhance the utility of expression system. This review illustrates heterologous expression of highly thermostable fungal cellulases especially focused on thermophilic endoglucanases, cellobiohydrolases and β-glucosidases in P. pastoris.