초록
The cellobiohydrolase II (CBH II) gene cbh2 from Trichoderma reesei was cloned and its codons were optimized in accordance with the codon usage frequencies of the host Pichia pastoris. The AOX1 strong promoter inducible by methanol was employed to efficiently express the foreign gene cbh2 in P. pastoris. It was found that 5.84 +/- 0.42 U cm<SUP>-3</SUP> CBH II was obtained at 96 h using the synthetic cbh2 gene whose codons were optimized, 2.02-fold higher than using the native cbh2 gene (2.89 +/- 0.32 U cm<SUP>-3</SUP>), indicating that the codon optimization strategy was an effective approach to enhance the heterologous expression of CBH II in P. pastoris. The product of recombinant P. pastoris CBH II had an approximate molecular weight 58 kDa. Its optimal pH and temperature were 5.0 and 50 <SUP>o</SUP>C, respectively. The recombinant CBH II was used to enhance the yields of the enzymatic hydrolysis of the corn stover and rice straw pretreated with sodium hydroxide by improving the exo-exo-synergism between CBH II and CBH I in T. reesei cellulase. The yields 94.7% and 83.3% were achieved in the enzymatic hydrolysis of corn stover and rice straw pretreated by sodium hydroxide, respectively.