High activity expression of d-amino acid oxidase in Escherichia coli by the protein expression rate optimization

► With RBS substitution, soluble DAAO expression was increased over 2-fold under T7 promoter. ► Constitutive expression system with Tac promoter and optimal RBS improved DAAO activity 20-fold. ► Expression rate optimization proved effective in the expression of other emzymes GCA and D-case.