Here, CelA is the most abundant enzyme secreted by <
i>
Caldicellulosiruptor bescii<
/i>
and has been shown to outperform mixtures of commercially available exo- and endoglucanases in vitro. CelA contains both a glycoside hydrolase family 9 endoglucanase and a glycoside hydrolase family 48 exoglucanase known to be synergistic in their activity, connected by three cellulose-binding domains via linker peptides. Here, repeated aspartate residues were introduced into the <
i>
N<
/i>
-terminal ends of CelA GH9 and GH48 domains to improve secretion efficiency and/or catalytic efficiency of CelA. Among several constructs, the highest activity on carboxymethylcellulose (CMC), 0.81 � 0.03 mg/mL was observed for the <
i>
C. bescii<
/i>
strain containing CelA with 5-aspartate tag at the N-terminal end of GH9 domain ? an 82% increase over wild type CelA. In addition, Expression of CelA with <
i>
N<
/i>
-terminal repeated aspartate residues in <
i>
C. bescii<
/i>
results in a dramatic increase in its ability to grow on Avicel.