Overexpression of squalene-hopene cyclase by the pET vector in Escherichia coli and first identification of tryptophan and aspartic acid residues inside the QW motif as active sites.

An overexpression system for squalene-hopene cyclase (SHC) was constructed by using the pET3a vector, which is responsible for high expression with help from the strong T7 promoter when incorporated into E. coli BL21(DE3). Site-directed mutagenesis experiments prove that two amino acid residues of tryptophan and aspartic acid inside the QW-motif 5 resided as active sites.