Cloning, Sequencing, and Expression of a Thermostable Cellulase Gene of Humicola grisea

Abstract

The egl2 gene encoding a thermostable endoglucanase (EGL2) was cloned from Humicola grisea. The DNA sequence of egl2 predicted two putative introns in the coding region. The deduced amino acid sequence of EGL2 was 388 amino acids in length and showed 99.5% identity with the H. insolens CMC 3. In addition to TATA box and CAAT motifs, putative CREA binding sites were observed in the 5' upstream region of the egl2 gene. The egl2 gene was expressed in Aspergillus oryzae, and EGL2 was purified. EGL2 produced by A. oryzae showed a high activity toward carboxymethyl cellulose. The optimal temperature of EGL2 was 75°C, and EGL2 had more than 80% residual activity after heating up to 75°C for 10 min. This is the first report of enzymatic properties of the EGL2-type thermostable cellulase homologs from Humicola.