Improvement of the Expression Level of beta-Glucosidase from Agrobacterium sp in Escherichia coli by Rare Codon Optimization

To achieve high level expression of beta-glucosidase from Agrobacterium sp. (Abg) in an Escherichia coli expression system, 6 rare codons at +3, +11, +158, +308, +314, and +318 of abg gene were replaced with favored codons using site-directed mutagenesis. The rare codon replacements of +3 (CCC) and +11 (CCC) positions enhanced the expression level of Abg by 2- and 3.6-fold, respectively. The double mutant, Abg-DM, where both of +3 and +11 rare codon positions were modified showed a 5.2-fold higher expression level than the original abg gene. Circular dichroism (CD) spectra of the over-expressed Abg and original Abg enzymes were identical, indicating that Abg was properly folded during over-expression.