Expression and characterization of the celcflB gene from Cellulomonas flavigena encoding an endo-β-1,4-glucanase

An endoglucanase gene called celcflB was isolated from a genomic library of C. flavigena. Its nucleotide sequence showed an ORF of 1725 bp with a GTG start codon. A promoter sequence was found inside the adjacent gene upstream from the start point of translation of celcflB gene. The gene celcflB was induced by sugarcane bagasse and repressed by glucose when C. flavigena was grown on these carbon sources, suggesting that celcflB gene is regulated at transcriptional level. The predicted amino acid sequence of the CelcflB protein presented a catalytic domain with a high homology to family 5 of glycosil hydrolases, and a cellulose binding domain identical to cellulose binding domains type II. The coding region of the celcflB gene was cloned into the expression vector pQE30 and the recombinant protein of 58 kDa presented endoglucanase activity towards carboxymethyl cellulose (CMC).