Display of active enzymes on the cell surface of Escherichia coli using PgsA anchor protein and their application to bioconversion

We have developed a novel Escherichia coli cell surface display system by employing PgsA as an anchoring motif. In our display system, C-terminal fusion to PgsA anchor protein from Bacillus subtilis was used. The enzymes selected for display were alpha-amylase (AmyA) from Streptococcus bovis 148 and lipase B (CALB) from Candida antarctica. The molecular mass values of AmyA and CALB are approximately 77 and 34 kDa, respectively. The enzymes were displayed on the surface as a fusion protein with a FLAG peptide tag at the C terminus. Both the PgsA-AmyA-FLAG and PgsA-CALB-FLAG fusion proteins were shown to be displayed by immunofluorescence labeling using anti-FLAG antibody. The displayed enzymes were active forms, and AmyA and CALB activities reached 990 U/g (dry cell weight) and 4.6 U/g (dry cell weight), respectively. AmyA-displaying E. coli cells grew utilizing cornstarch as the sole carbon source, while CALB-displaying E. coli cells catalyzed enantioselective transesterification, indicating that they are effective whole-cell biocatalysts. Since a target enzyme with a size of 77 kDa and an industrially useful lipase have been successfully displayed on the cell surface of E. coli for the first time, PgsA protein is probably a useful anchoring motif to display various enzymes.